# sqlglot.transforms API documentation

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# sqlglot.transforms

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      1from __future__ import annotations
      2
      3import typing as t
      4
      5from sqlglot import expressions as exp
      6from sqlglot.helper import find_new_name, name_sequence
      7
      8if t.TYPE_CHECKING:
      9    from sqlglot.generator import Generator
     10
     11
     12def unalias_group(expression: exp.Expression) -> exp.Expression:
     13    """
     14    Replace references to select aliases in GROUP BY clauses.
     15
     16    Example:
     17        >>> import sqlglot
     18        >>> sqlglot.parse_one("SELECT a AS b FROM x GROUP BY b").transform(unalias_group).sql()
     19        'SELECT a AS b FROM x GROUP BY 1'
     20
     21    Args:
     22        expression: the expression that will be transformed.
     23
     24    Returns:
     25        The transformed expression.
     26    """
     27    if isinstance(expression, exp.Group) and isinstance(expression.parent, exp.Select):
     28        aliased_selects = {
     29            e.alias: i
     30            for i, e in enumerate(expression.parent.expressions, start=1)
     31            if isinstance(e, exp.Alias)
     32        }
     33
     34        for group_by in expression.expressions:
     35            if (
     36                isinstance(group_by, exp.Column)
     37                and not group_by.table
     38                and group_by.name in aliased_selects
     39            ):
     40                group_by.replace(exp.Literal.number(aliased_selects.get(group_by.name)))
     41
     42    return expression
     43
     44
     45def eliminate_distinct_on(expression: exp.Expression) -> exp.Expression:
     46    """
     47    Convert SELECT DISTINCT ON statements to a subquery with a window function.
     48
     49    This is useful for dialects that don't support SELECT DISTINCT ON but support window functions.
     50
     51    Args:
     52        expression: the expression that will be transformed.
     53
     54    Returns:
     55        The transformed expression.
     56    """
     57    if (
     58        isinstance(expression, exp.Select)
     59        and expression.args.get("distinct")
     60        and expression.args["distinct"].args.get("on")
     61        and isinstance(expression.args["distinct"].args["on"], exp.Tuple)
     62    ):
     63        distinct_cols = expression.args["distinct"].pop().args["on"].expressions
     64        outer_selects = expression.selects
     65        row_number = find_new_name(expression.named_selects, "_row_number")
     66        window = exp.Window(this=exp.RowNumber(), partition_by=distinct_cols)
     67        order = expression.args.get("order")
     68
     69        if order:
     70            window.set("order", order.pop())
     71        else:
     72            window.set("order", exp.Order(expressions=[c.copy() for c in distinct_cols]))
     73
     74        window = exp.alias_(window, row_number)
     75        expression.select(window, copy=False)
     76
     77        return (
     78            exp.select(*outer_selects, copy=False)
     79            .from_(expression.subquery("_t", copy=False), copy=False)
     80            .where(exp.column(row_number).eq(1), copy=False)
     81        )
     82
     83    return expression
     84
     85
     86def eliminate_qualify(expression: exp.Expression) -> exp.Expression:
     87    """
     88    Convert SELECT statements that contain the QUALIFY clause into subqueries, filtered equivalently.
     89
     90    The idea behind this transformation can be seen in Snowflake's documentation for QUALIFY:
     91    https://docs.snowflake.com/en/sql-reference/constructs/qualify
     92
     93    Some dialects don't support window functions in the WHERE clause, so we need to include them as
     94    projections in the subquery, in order to refer to them in the outer filter using aliases. Also,
     95    if a column is referenced in the QUALIFY clause but is not selected, we need to include it too,
     96    otherwise we won't be able to refer to it in the outer query's WHERE clause.
     97    """
     98    if isinstance(expression, exp.Select) and expression.args.get("qualify"):
     99        taken = set(expression.named_selects)
    100        for select in expression.selects:
    101            if not select.alias_or_name:
    102                alias = find_new_name(taken, "_c")
    103                select.replace(exp.alias_(select, alias))
    104                taken.add(alias)
    105
    106        outer_selects = exp.select(*[select.alias_or_name for select in expression.selects])
    107        qualify_filters = expression.args["qualify"].pop().this
    108
    109        select_candidates = exp.Window if expression.is_star else (exp.Window, exp.Column)
    110        for expr in qualify_filters.find_all(select_candidates):
    111            if isinstance(expr, exp.Window):
    112                alias = find_new_name(expression.named_selects, "_w")
    113                expression.select(exp.alias_(expr, alias), copy=False)
    114                column = exp.column(alias)
    115
    116                if isinstance(expr.parent, exp.Qualify):
    117                    qualify_filters = column
    118                else:
    119                    expr.replace(column)
    120            elif expr.name not in expression.named_selects:
    121                expression.select(expr.copy(), copy=False)
    122
    123        return outer_selects.from_(expression.subquery(alias="_t", copy=False), copy=False).where(
    124            qualify_filters, copy=False
    125        )
    126
    127    return expression
    128
    129
    130def remove_precision_parameterized_types(expression: exp.Expression) -> exp.Expression:
    131    """
    132    Some dialects only allow the precision for parameterized types to be defined in the DDL and not in
    133    other expressions. This transforms removes the precision from parameterized types in expressions.
    134    """
    135    for node in expression.find_all(exp.DataType):
    136        node.set(
    137            "expressions", [e for e in node.expressions if not isinstance(e, exp.DataTypeParam)]
    138        )
    139
    140    return expression
    141
    142
    143def unnest_to_explode(expression: exp.Expression) -> exp.Expression:
    144    """Convert cross join unnest into lateral view explode."""
    145    if isinstance(expression, exp.Select):
    146        for join in expression.args.get("joins") or []:
    147            unnest = join.this
    148
    149            if isinstance(unnest, exp.Unnest):
    150                alias = unnest.args.get("alias")
    151                udtf = exp.Posexplode if unnest.args.get("offset") else exp.Explode
    152
    153                expression.args["joins"].remove(join)
    154
    155                for e, column in zip(unnest.expressions, alias.columns if alias else []):
    156                    expression.append(
    157                        "laterals",
    158                        exp.Lateral(
    159                            this=udtf(this=e),
    160                            view=True,
    161                            alias=exp.TableAlias(this=alias.this, columns=[column]),  # type: ignore
    162                        ),
    163                    )
    164
    165    return expression
    166
    167
    168def explode_to_unnest(index_offset: int = 0) -> t.Callable[[exp.Expression], exp.Expression]:
    169    """Convert explode/posexplode into unnest."""
    170
    171    def _explode_to_unnest(expression: exp.Expression) -> exp.Expression:
    172        if isinstance(expression, exp.Select):
    173            from sqlglot.optimizer.scope import Scope
    174
    175            taken_select_names = set(expression.named_selects)
    176            taken_source_names = {name for name, _ in Scope(expression).references}
    177
    178            def new_name(names: t.Set[str], name: str) -> str:
    179                name = find_new_name(names, name)
    180                names.add(name)
    181                return name
    182
    183            arrays: t.List[exp.Condition] = []
    184            series_alias = new_name(taken_select_names, "pos")
    185            series = exp.alias_(
    186                exp.Unnest(
    187                    expressions=[exp.GenerateSeries(start=exp.Literal.number(index_offset))]
    188                ),
    189                new_name(taken_source_names, "_u"),
    190                table=[series_alias],
    191            )
    192
    193            # we use list here because expression.selects is mutated inside the loop
    194            for select in list(expression.selects):
    195                explode = select.find(exp.Explode)
    196
    197                if explode:
    198                    pos_alias = ""
    199                    explode_alias = ""
    200
    201                    if isinstance(select, exp.Alias):
    202                        explode_alias = select.args["alias"]
    203                        alias = select
    204                    elif isinstance(select, exp.Aliases):
    205                        pos_alias = select.aliases[0]
    206                        explode_alias = select.aliases[1]
    207                        alias = select.replace(exp.alias_(select.this, "", copy=False))
    208                    else:
    209                        alias = select.replace(exp.alias_(select, ""))
    210                        explode = alias.find(exp.Explode)
    211                        assert explode
    212
    213                    is_posexplode = isinstance(explode, exp.Posexplode)
    214                    explode_arg = explode.this
    215
    216                    # This ensures that we won't use [POS]EXPLODE's argument as a new selection
    217                    if isinstance(explode_arg, exp.Column):
    218                        taken_select_names.add(explode_arg.output_name)
    219
    220                    unnest_source_alias = new_name(taken_source_names, "_u")
    221
    222                    if not explode_alias:
    223                        explode_alias = new_name(taken_select_names, "col")
    224
    225                        if is_posexplode:
    226                            pos_alias = new_name(taken_select_names, "pos")
    227
    228                    if not pos_alias:
    229                        pos_alias = new_name(taken_select_names, "pos")
    230
    231                    alias.set("alias", exp.to_identifier(explode_alias))
    232
    233                    series_table_alias = series.args["alias"].this
    234                    column = exp.If(
    235                        this=exp.column(series_alias, table=series_table_alias).eq(
    236                            exp.column(pos_alias, table=unnest_source_alias)
    237                        ),
    238                        true=exp.column(explode_alias, table=unnest_source_alias),
    239                    )
    240
    241                    explode.replace(column)
    242
    243                    if is_posexplode:
    244                        expressions = expression.expressions
    245                        expressions.insert(
    246                            expressions.index(alias) + 1,
    247                            exp.If(
    248                                this=exp.column(series_alias, table=series_table_alias).eq(
    249                                    exp.column(pos_alias, table=unnest_source_alias)
    250                                ),
    251                                true=exp.column(pos_alias, table=unnest_source_alias),
    252                            ).as_(pos_alias),
    253                        )
    254                        expression.set("expressions", expressions)
    255
    256                    if not arrays:
    257                        if expression.args.get("from"):
    258                            expression.join(series, copy=False, join_type="CROSS")
    259                        else:
    260                            expression.from_(series, copy=False)
    261
    262                    size: exp.Condition = exp.ArraySize(this=explode_arg.copy())
    263                    arrays.append(size)
    264
    265                    # trino doesn't support left join unnest with on conditions
    266                    # if it did, this would be much simpler
    267                    expression.join(
    268                        exp.alias_(
    269                            exp.Unnest(
    270                                expressions=[explode_arg.copy()],
    271                                offset=exp.to_identifier(pos_alias),
    272                            ),
    273                            unnest_source_alias,
    274                            table=[explode_alias],
    275                        ),
    276                        join_type="CROSS",
    277                        copy=False,
    278                    )
    279
    280                    if index_offset != 1:
    281                        size = size - 1
    282
    283                    expression.where(
    284                        exp.column(series_alias, table=series_table_alias)
    285                        .eq(exp.column(pos_alias, table=unnest_source_alias))
    286                        .or_(
    287                            (exp.column(series_alias, table=series_table_alias) > size).and_(
    288                                exp.column(pos_alias, table=unnest_source_alias).eq(size)
    289                            )
    290                        ),
    291                        copy=False,
    292                    )
    293
    294            if arrays:
    295                end: exp.Condition = exp.Greatest(this=arrays[0], expressions=arrays[1:])
    296
    297                if index_offset != 1:
    298                    end = end - (1 - index_offset)
    299                series.expressions[0].set("end", end)
    300
    301        return expression
    302
    303    return _explode_to_unnest
    304
    305
    306PERCENTILES = (exp.PercentileCont, exp.PercentileDisc)
    307
    308
    309def add_within_group_for_percentiles(expression: exp.Expression) -> exp.Expression:
    310    """Transforms percentiles by adding a WITHIN GROUP clause to them."""
    311    if (
    312        isinstance(expression, PERCENTILES)
    313        and not isinstance(expression.parent, exp.WithinGroup)
    314        and expression.expression
    315    ):
    316        column = expression.this.pop()
    317        expression.set("this", expression.expression.pop())
    318        order = exp.Order(expressions=[exp.Ordered(this=column)])
    319        expression = exp.WithinGroup(this=expression, expression=order)
    320
    321    return expression
    322
    323
    324def remove_within_group_for_percentiles(expression: exp.Expression) -> exp.Expression:
    325    """Transforms percentiles by getting rid of their corresponding WITHIN GROUP clause."""
    326    if (
    327        isinstance(expression, exp.WithinGroup)
    328        and isinstance(expression.this, PERCENTILES)
    329        and isinstance(expression.expression, exp.Order)
    330    ):
    331        quantile = expression.this.this
    332        input_value = t.cast(exp.Ordered, expression.find(exp.Ordered)).this
    333        return expression.replace(exp.ApproxQuantile(this=input_value, quantile=quantile))
    334
    335    return expression
    336
    337
    338def add_recursive_cte_column_names(expression: exp.Expression) -> exp.Expression:
    339    """Uses projection output names in recursive CTE definitions to define the CTEs' columns."""
    340    if isinstance(expression, exp.With) and expression.recursive:
    341        next_name = name_sequence("_c_")
    342
    343        for cte in expression.expressions:
    344            if not cte.args["alias"].columns:
    345                query = cte.this
    346                if isinstance(query, exp.Union):
    347                    query = query.this
    348
    349                cte.args["alias"].set(
    350                    "columns",
    351                    [exp.to_identifier(s.alias_or_name or next_name()) for s in query.selects],
    352                )
    353
    354    return expression
    355
    356
    357def epoch_cast_to_ts(expression: exp.Expression) -> exp.Expression:
    358    """Replace 'epoch' in casts by the equivalent date literal."""
    359    if (
    360        isinstance(expression, (exp.Cast, exp.TryCast))
    361        and expression.name.lower() == "epoch"
    362        and expression.to.this in exp.DataType.TEMPORAL_TYPES
    363    ):
    364        expression.this.replace(exp.Literal.string("1970-01-01 00:00:00"))
    365
    366    return expression
    367
    368
    369def eliminate_semi_and_anti_joins(expression: exp.Expression) -> exp.Expression:
    370    """Convert SEMI and ANTI joins into equivalent forms that use EXIST instead."""
    371    if isinstance(expression, exp.Select):
    372        for join in expression.args.get("joins") or []:
    373            on = join.args.get("on")
    374            if on and join.kind in ("SEMI", "ANTI"):
    375                subquery = exp.select("1").from_(join.this).where(on)
    376                exists = exp.Exists(this=subquery)
    377                if join.kind == "ANTI":
    378                    exists = exists.not_(copy=False)
    379
    380                join.pop()
    381                expression.where(exists, copy=False)
    382
    383    return expression
    384
    385
    386def eliminate_full_outer_join(expression: exp.Expression) -> exp.Expression:
    387    """
    388    Converts a query with a FULL OUTER join to a union of identical queries that
    389    use LEFT/RIGHT OUTER joins instead. This transformation currently only works
    390    for queries that have a single FULL OUTER join.
    391    """
    392    if isinstance(expression, exp.Select):
    393        full_outer_joins = [
    394            (index, join)
    395            for index, join in enumerate(expression.args.get("joins") or [])
    396            if join.side == "FULL"
    397        ]
    398
    399        if len(full_outer_joins) == 1:
    400            expression_copy = expression.copy()
    401            expression.set("limit", None)
    402            index, full_outer_join = full_outer_joins[0]
    403            full_outer_join.set("side", "left")
    404            expression_copy.args["joins"][index].set("side", "right")
    405            expression_copy.args.pop("with", None)  # remove CTEs from RIGHT side
    406
    407            return exp.union(expression, expression_copy, copy=False)
    408
    409    return expression
    410
    411
    412def move_ctes_to_top_level(expression: exp.Expression) -> exp.Expression:
    413    """
    414    Some dialects (e.g. Hive, T-SQL, Spark prior to version 3) only allow CTEs to be
    415    defined at the top-level, so for example queries like:
    416
    417        SELECT * FROM (WITH t(c) AS (SELECT 1) SELECT * FROM t) AS subq
    418
    419    are invalid in those dialects. This transformation can be used to ensure all CTEs are
    420    moved to the top level so that the final SQL code is valid from a syntax standpoint.
    421
    422    TODO: handle name clashes whilst moving CTEs (it can get quite tricky & costly).
    423    """
    424    top_level_with = expression.args.get("with")
    425    for node in expression.find_all(exp.With):
    426        if node.parent is expression:
    427            continue
    428
    429        inner_with = node.pop()
    430        if not top_level_with:
    431            top_level_with = inner_with
    432            expression.set("with", top_level_with)
    433        else:
    434            if inner_with.recursive:
    435                top_level_with.set("recursive", True)
    436
    437            top_level_with.expressions.extend(inner_with.expressions)
    438
    439    return expression
    440
    441
    442def ensure_bools(expression: exp.Expression) -> exp.Expression:
    443    """Converts numeric values used in conditions into explicit boolean expressions."""
    444    from sqlglot.optimizer.canonicalize import ensure_bools
    445
    446    def _ensure_bool(node: exp.Expression) -> None:
    447        if (
    448            node.is_number
    449            or node.is_type(exp.DataType.Type.UNKNOWN, *exp.DataType.NUMERIC_TYPES)
    450            or (isinstance(node, exp.Column) and not node.type)
    451        ):
    452            node.replace(node.neq(0))
    453
    454    for node, *_ in expression.walk():
    455        ensure_bools(node, _ensure_bool)
    456
    457    return expression
    458
    459
    460def unqualify_columns(expression: exp.Expression) -> exp.Expression:
    461    for column in expression.find_all(exp.Column):
    462        # We only wanna pop off the table, db, catalog args
    463        for part in column.parts[:-1]:
    464            part.pop()
    465
    466    return expression
    467
    468
    469def preprocess(
    470    transforms: t.List[t.Callable[[exp.Expression], exp.Expression]],
    471) -> t.Callable[[Generator, exp.Expression], str]:
    472    """
    473    Creates a new transform by chaining a sequence of transformations and converts the resulting
    474    expression to SQL, using either the "_sql" method corresponding to the resulting expression,
    475    or the appropriate `Generator.TRANSFORMS` function (when applicable -- see below).
    476
    477    Args:
    478        transforms: sequence of transform functions. These will be called in order.
    479
    480    Returns:
    481        Function that can be used as a generator transform.
    482    """
    483
    484    def _to_sql(self, expression: exp.Expression) -> str:
    485        expression_type = type(expression)
    486
    487        expression = transforms[0](expression)
    488        for transform in transforms[1:]:
    489            expression = transform(expression)
    490
    491        _sql_handler = getattr(self, expression.key + "_sql", None)
    492        if _sql_handler:
    493            return _sql_handler(expression)
    494
    495        transforms_handler = self.TRANSFORMS.get(type(expression))
    496        if transforms_handler:
    497            if expression_type is type(expression):
    498                if isinstance(expression, exp.Func):
    499                    return self.function_fallback_sql(expression)
    500
    501                # Ensures we don't enter an infinite loop. This can happen when the original expression
    502                # has the same type as the final expression and there's no _sql method available for it,
    503                # because then it'd re-enter _to_sql.
    504                raise ValueError(
    505                    f"Expression type {expression.__class__.__name__} requires a _sql method in order to be transformed."
    506                )
    507
    508            return transforms_handler(self, expression)
    509
    510        raise ValueError(f"Unsupported expression type {expression.__class__.__name__}.")
    511
    512    return _to_sql

def unalias_group( expression: sqlglot.expressions.Expression ) -> sqlglot.expressions.Expression: View Source

    13def unalias_group(expression: exp.Expression) -> exp.Expression:
    14    """
    15    Replace references to select aliases in GROUP BY clauses.
    16
    17    Example:
    18        >>> import sqlglot
    19        >>> sqlglot.parse_one("SELECT a AS b FROM x GROUP BY b").transform(unalias_group).sql()
    20        'SELECT a AS b FROM x GROUP BY 1'
    21
    22    Args:
    23        expression: the expression that will be transformed.
    24
    25    Returns:
    26        The transformed expression.
    27    """
    28    if isinstance(expression, exp.Group) and isinstance(expression.parent, exp.Select):
    29        aliased_selects = {
    30            e.alias: i
    31            for i, e in enumerate(expression.parent.expressions, start=1)
    32            if isinstance(e, exp.Alias)
    33        }
    34
    35        for group_by in expression.expressions:
    36            if (
    37                isinstance(group_by, exp.Column)
    38                and not group_by.table
    39                and group_by.name in aliased_selects
    40            ):
    41                group_by.replace(exp.Literal.number(aliased_selects.get(group_by.name)))
    42
    43    return expression

Replace references to select aliases in GROUP BY clauses.

###### Example:

>     >>> import sqlglot
>     >>> sqlglot.parse_one("SELECT a AS b FROM x GROUP BY b").transform(unalias_group).sql()
>     'SELECT a AS b FROM x GROUP BY 1'

###### Arguments:

- expression: the expression that will be transformed.

###### Returns:

> The transformed expression.

def eliminate_distinct_on( expression: sqlglot.expressions.Expression ) -> sqlglot.expressions.Expression: View Source

    46def eliminate_distinct_on(expression: exp.Expression) -> exp.Expression:
    47    """
    48    Convert SELECT DISTINCT ON statements to a subquery with a window function.
    49
    50    This is useful for dialects that don't support SELECT DISTINCT ON but support window functions.
    51
    52    Args:
    53        expression: the expression that will be transformed.
    54
    55    Returns:
    56        The transformed expression.
    57    """
    58    if (
    59        isinstance(expression, exp.Select)
    60        and expression.args.get("distinct")
    61        and expression.args["distinct"].args.get("on")
    62        and isinstance(expression.args["distinct"].args["on"], exp.Tuple)
    63    ):
    64        distinct_cols = expression.args["distinct"].pop().args["on"].expressions
    65        outer_selects = expression.selects
    66        row_number = find_new_name(expression.named_selects, "_row_number")
    67        window = exp.Window(this=exp.RowNumber(), partition_by=distinct_cols)
    68        order = expression.args.get("order")
    69
    70        if order:
    71            window.set("order", order.pop())
    72        else:
    73            window.set("order", exp.Order(expressions=[c.copy() for c in distinct_cols]))
    74
    75        window = exp.alias_(window, row_number)
    76        expression.select(window, copy=False)
    77
    78        return (
    79            exp.select(*outer_selects, copy=False)
    80            .from_(expression.subquery("_t", copy=False), copy=False)
    81            .where(exp.column(row_number).eq(1), copy=False)
    82        )
    83
    84    return expression

Convert SELECT DISTINCT ON statements to a subquery with a window function.

This is useful for dialects that don't support SELECT DISTINCT ON but support window functions.

###### Arguments:

- expression: the expression that will be transformed.

###### Returns:

> The transformed expression.

def eliminate_qualify( expression: sqlglot.expressions.Expression ) -> sqlglot.expressions.Expression: View Source

     87def eliminate_qualify(expression: exp.Expression) -> exp.Expression:
     88    """
     89    Convert SELECT statements that contain the QUALIFY clause into subqueries, filtered equivalently.
     90
     91    The idea behind this transformation can be seen in Snowflake's documentation for QUALIFY:
     92    https://docs.snowflake.com/en/sql-reference/constructs/qualify
     93
     94    Some dialects don't support window functions in the WHERE clause, so we need to include them as
     95    projections in the subquery, in order to refer to them in the outer filter using aliases. Also,
     96    if a column is referenced in the QUALIFY clause but is not selected, we need to include it too,
     97    otherwise we won't be able to refer to it in the outer query's WHERE clause.
     98    """
     99    if isinstance(expression, exp.Select) and expression.args.get("qualify"):
    100        taken = set(expression.named_selects)
    101        for select in expression.selects:
    102            if not select.alias_or_name:
    103                alias = find_new_name(taken, "_c")
    104                select.replace(exp.alias_(select, alias))
    105                taken.add(alias)
    106
    107        outer_selects = exp.select(*[select.alias_or_name for select in expression.selects])
    108        qualify_filters = expression.args["qualify"].pop().this
    109
    110        select_candidates = exp.Window if expression.is_star else (exp.Window, exp.Column)
    111        for expr in qualify_filters.find_all(select_candidates):
    112            if isinstance(expr, exp.Window):
    113                alias = find_new_name(expression.named_selects, "_w")
    114                expression.select(exp.alias_(expr, alias), copy=False)
    115                column = exp.column(alias)
    116
    117                if isinstance(expr.parent, exp.Qualify):
    118                    qualify_filters = column
    119                else:
    120                    expr.replace(column)
    121            elif expr.name not in expression.named_selects:
    122                expression.select(expr.copy(), copy=False)
    123
    124        return outer_selects.from_(expression.subquery(alias="_t", copy=False), copy=False).where(
    125            qualify_filters, copy=False
    126        )
    127
    128    return expression

Convert SELECT statements that contain the QUALIFY clause into subqueries, filtered equivalently.

The idea behind this transformation can be seen in Snowflake's documentation for QUALIFY: https://docs.snowflake.com/en/sql-reference/constructs/qualify

Some dialects don't support window functions in the WHERE clause, so we need to include them as projections in the subquery, in order to refer to them in the outer filter using aliases. Also, if a column is referenced in the QUALIFY clause but is not selected, we need to include it too, otherwise we won't be able to refer to it in the outer query's WHERE clause.

def remove_precision_parameterized_types( expression: sqlglot.expressions.Expression ) -> sqlglot.expressions.Expression: View Source

    131def remove_precision_parameterized_types(expression: exp.Expression) -> exp.Expression:
    132    """
    133    Some dialects only allow the precision for parameterized types to be defined in the DDL and not in
    134    other expressions. This transforms removes the precision from parameterized types in expressions.
    135    """
    136    for node in expression.find_all(exp.DataType):
    137        node.set(
    138            "expressions", [e for e in node.expressions if not isinstance(e, exp.DataTypeParam)]
    139        )
    140
    141    return expression

Some dialects only allow the precision for parameterized types to be defined in the DDL and not in other expressions. This transforms removes the precision from parameterized types in expressions.

def unnest_to_explode( expression: sqlglot.expressions.Expression ) -> sqlglot.expressions.Expression: View Source

    144def unnest_to_explode(expression: exp.Expression) -> exp.Expression:
    145    """Convert cross join unnest into lateral view explode."""
    146    if isinstance(expression, exp.Select):
    147        for join in expression.args.get("joins") or []:
    148            unnest = join.this
    149
    150            if isinstance(unnest, exp.Unnest):
    151                alias = unnest.args.get("alias")
    152                udtf = exp.Posexplode if unnest.args.get("offset") else exp.Explode
    153
    154                expression.args["joins"].remove(join)
    155
    156                for e, column in zip(unnest.expressions, alias.columns if alias else []):
    157                    expression.append(
    158                        "laterals",
    159                        exp.Lateral(
    160                            this=udtf(this=e),
    161                            view=True,
    162                            alias=exp.TableAlias(this=alias.this, columns=[column]),  # type: ignore
    163                        ),
    164                    )
    165
    166    return expression

Convert cross join unnest into lateral view explode.

def explode_to_unnest( index_offset: int = 0) -> Callable[[ sqlglot.expressions.Expression ], sqlglot.expressions.Expression ]: View Source

    169def explode_to_unnest(index_offset: int = 0) -> t.Callable[[exp.Expression], exp.Expression]:
    170    """Convert explode/posexplode into unnest."""
    171
    172    def _explode_to_unnest(expression: exp.Expression) -> exp.Expression:
    173        if isinstance(expression, exp.Select):
    174            from sqlglot.optimizer.scope import Scope
    175
    176            taken_select_names = set(expression.named_selects)
    177            taken_source_names = {name for name, _ in Scope(expression).references}
    178
    179            def new_name(names: t.Set[str], name: str) -> str:
    180                name = find_new_name(names, name)
    181                names.add(name)
    182                return name
    183
    184            arrays: t.List[exp.Condition] = []
    185            series_alias = new_name(taken_select_names, "pos")
    186            series = exp.alias_(
    187                exp.Unnest(
    188                    expressions=[exp.GenerateSeries(start=exp.Literal.number(index_offset))]
    189                ),
    190                new_name(taken_source_names, "_u"),
    191                table=[series_alias],
    192            )
    193
    194            # we use list here because expression.selects is mutated inside the loop
    195            for select in list(expression.selects):
    196                explode = select.find(exp.Explode)
    197
    198                if explode:
    199                    pos_alias = ""
    200                    explode_alias = ""
    201
    202                    if isinstance(select, exp.Alias):
    203                        explode_alias = select.args["alias"]
    204                        alias = select
    205                    elif isinstance(select, exp.Aliases):
    206                        pos_alias = select.aliases[0]
    207                        explode_alias = select.aliases[1]
    208                        alias = select.replace(exp.alias_(select.this, "", copy=False))
    209                    else:
    210                        alias = select.replace(exp.alias_(select, ""))
    211                        explode = alias.find(exp.Explode)
    212                        assert explode
    213
    214                    is_posexplode = isinstance(explode, exp.Posexplode)
    215                    explode_arg = explode.this
    216
    217                    # This ensures that we won't use [POS]EXPLODE's argument as a new selection
    218                    if isinstance(explode_arg, exp.Column):
    219                        taken_select_names.add(explode_arg.output_name)
    220
    221                    unnest_source_alias = new_name(taken_source_names, "_u")
    222
    223                    if not explode_alias:
    224                        explode_alias = new_name(taken_select_names, "col")
    225
    226                        if is_posexplode:
    227                            pos_alias = new_name(taken_select_names, "pos")
    228
    229                    if not pos_alias:
    230                        pos_alias = new_name(taken_select_names, "pos")
    231
    232                    alias.set("alias", exp.to_identifier(explode_alias))
    233
    234                    series_table_alias = series.args["alias"].this
    235                    column = exp.If(
    236                        this=exp.column(series_alias, table=series_table_alias).eq(
    237                            exp.column(pos_alias, table=unnest_source_alias)
    238                        ),
    239                        true=exp.column(explode_alias, table=unnest_source_alias),
    240                    )
    241
    242                    explode.replace(column)
    243
    244                    if is_posexplode:
    245                        expressions = expression.expressions
    246                        expressions.insert(
    247                            expressions.index(alias) + 1,
    248                            exp.If(
    249                                this=exp.column(series_alias, table=series_table_alias).eq(
    250                                    exp.column(pos_alias, table=unnest_source_alias)
    251                                ),
    252                                true=exp.column(pos_alias, table=unnest_source_alias),
    253                            ).as_(pos_alias),
    254                        )
    255                        expression.set("expressions", expressions)
    256
    257                    if not arrays:
    258                        if expression.args.get("from"):
    259                            expression.join(series, copy=False, join_type="CROSS")
    260                        else:
    261                            expression.from_(series, copy=False)
    262
    263                    size: exp.Condition = exp.ArraySize(this=explode_arg.copy())
    264                    arrays.append(size)
    265
    266                    # trino doesn't support left join unnest with on conditions
    267                    # if it did, this would be much simpler
    268                    expression.join(
    269                        exp.alias_(
    270                            exp.Unnest(
    271                                expressions=[explode_arg.copy()],
    272                                offset=exp.to_identifier(pos_alias),
    273                            ),
    274                            unnest_source_alias,
    275                            table=[explode_alias],
    276                        ),
    277                        join_type="CROSS",
    278                        copy=False,
    279                    )
    280
    281                    if index_offset != 1:
    282                        size = size - 1
    283
    284                    expression.where(
    285                        exp.column(series_alias, table=series_table_alias)
    286                        .eq(exp.column(pos_alias, table=unnest_source_alias))
    287                        .or_(
    288                            (exp.column(series_alias, table=series_table_alias) > size).and_(
    289                                exp.column(pos_alias, table=unnest_source_alias).eq(size)
    290                            )
    291                        ),
    292                        copy=False,
    293                    )
    294
    295            if arrays:
    296                end: exp.Condition = exp.Greatest(this=arrays[0], expressions=arrays[1:])
    297
    298                if index_offset != 1:
    299                    end = end - (1 - index_offset)
    300                series.expressions[0].set("end", end)
    301
    302        return expression
    303
    304    return _explode_to_unnest

Convert explode/posexplode into unnest.

PERCENTILES = (<class 'sqlglot.expressions.PercentileCont'>, <class 'sqlglot.expressions.PercentileDisc'>)
def add_within_group_for_percentiles( expression: sqlglot.expressions.Expression ) -> sqlglot.expressions.Expression: View Source

    310def add_within_group_for_percentiles(expression: exp.Expression) -> exp.Expression:
    311    """Transforms percentiles by adding a WITHIN GROUP clause to them."""
    312    if (
    313        isinstance(expression, PERCENTILES)
    314        and not isinstance(expression.parent, exp.WithinGroup)
    315        and expression.expression
    316    ):
    317        column = expression.this.pop()
    318        expression.set("this", expression.expression.pop())
    319        order = exp.Order(expressions=[exp.Ordered(this=column)])
    320        expression = exp.WithinGroup(this=expression, expression=order)
    321
    322    return expression

Transforms percentiles by adding a WITHIN GROUP clause to them.

def remove_within_group_for_percentiles( expression: sqlglot.expressions.Expression ) -> sqlglot.expressions.Expression: View Source

    325def remove_within_group_for_percentiles(expression: exp.Expression) -> exp.Expression:
    326    """Transforms percentiles by getting rid of their corresponding WITHIN GROUP clause."""
    327    if (
    328        isinstance(expression, exp.WithinGroup)
    329        and isinstance(expression.this, PERCENTILES)
    330        and isinstance(expression.expression, exp.Order)
    331    ):
    332        quantile = expression.this.this
    333        input_value = t.cast(exp.Ordered, expression.find(exp.Ordered)).this
    334        return expression.replace(exp.ApproxQuantile(this=input_value, quantile=quantile))
    335
    336    return expression

Transforms percentiles by getting rid of their corresponding WITHIN GROUP clause.

def add_recursive_cte_column_names( expression: sqlglot.expressions.Expression ) -> sqlglot.expressions.Expression: View Source

    339def add_recursive_cte_column_names(expression: exp.Expression) -> exp.Expression:
    340    """Uses projection output names in recursive CTE definitions to define the CTEs' columns."""
    341    if isinstance(expression, exp.With) and expression.recursive:
    342        next_name = name_sequence("_c_")
    343
    344        for cte in expression.expressions:
    345            if not cte.args["alias"].columns:
    346                query = cte.this
    347                if isinstance(query, exp.Union):
    348                    query = query.this
    349
    350                cte.args["alias"].set(
    351                    "columns",
    352                    [exp.to_identifier(s.alias_or_name or next_name()) for s in query.selects],
    353                )
    354
    355    return expression

Uses projection output names in recursive CTE definitions to define the CTEs' columns.

def epoch_cast_to_ts( expression: sqlglot.expressions.Expression ) -> sqlglot.expressions.Expression: View Source

    358def epoch_cast_to_ts(expression: exp.Expression) -> exp.Expression:
    359    """Replace 'epoch' in casts by the equivalent date literal."""
    360    if (
    361        isinstance(expression, (exp.Cast, exp.TryCast))
    362        and expression.name.lower() == "epoch"
    363        and expression.to.this in exp.DataType.TEMPORAL_TYPES
    364    ):
    365        expression.this.replace(exp.Literal.string("1970-01-01 00:00:00"))
    366
    367    return expression

Replace 'epoch' in casts by the equivalent date literal.

def eliminate_semi_and_anti_joins( expression: sqlglot.expressions.Expression ) -> sqlglot.expressions.Expression: View Source

    370def eliminate_semi_and_anti_joins(expression: exp.Expression) -> exp.Expression:
    371    """Convert SEMI and ANTI joins into equivalent forms that use EXIST instead."""
    372    if isinstance(expression, exp.Select):
    373        for join in expression.args.get("joins") or []:
    374            on = join.args.get("on")
    375            if on and join.kind in ("SEMI", "ANTI"):
    376                subquery = exp.select("1").from_(join.this).where(on)
    377                exists = exp.Exists(this=subquery)
    378                if join.kind == "ANTI":
    379                    exists = exists.not_(copy=False)
    380
    381                join.pop()
    382                expression.where(exists, copy=False)
    383
    384    return expression

Convert SEMI and ANTI joins into equivalent forms that use EXIST instead.

def eliminate_full_outer_join( expression: sqlglot.expressions.Expression ) -> sqlglot.expressions.Expression: View Source

    387def eliminate_full_outer_join(expression: exp.Expression) -> exp.Expression:
    388    """
    389    Converts a query with a FULL OUTER join to a union of identical queries that
    390    use LEFT/RIGHT OUTER joins instead. This transformation currently only works
    391    for queries that have a single FULL OUTER join.
    392    """
    393    if isinstance(expression, exp.Select):
    394        full_outer_joins = [
    395            (index, join)
    396            for index, join in enumerate(expression.args.get("joins") or [])
    397            if join.side == "FULL"
    398        ]
    399
    400        if len(full_outer_joins) == 1:
    401            expression_copy = expression.copy()
    402            expression.set("limit", None)
    403            index, full_outer_join = full_outer_joins[0]
    404            full_outer_join.set("side", "left")
    405            expression_copy.args["joins"][index].set("side", "right")
    406            expression_copy.args.pop("with", None)  # remove CTEs from RIGHT side
    407
    408            return exp.union(expression, expression_copy, copy=False)
    409
    410    return expression

Converts a query with a FULL OUTER join to a union of identical queries that use LEFT/RIGHT OUTER joins instead. This transformation currently only works for queries that have a single FULL OUTER join.

def move_ctes_to_top_level( expression: sqlglot.expressions.Expression ) -> sqlglot.expressions.Expression: View Source

    413def move_ctes_to_top_level(expression: exp.Expression) -> exp.Expression:
    414    """
    415    Some dialects (e.g. Hive, T-SQL, Spark prior to version 3) only allow CTEs to be
    416    defined at the top-level, so for example queries like:
    417
    418        SELECT * FROM (WITH t(c) AS (SELECT 1) SELECT * FROM t) AS subq
    419
    420    are invalid in those dialects. This transformation can be used to ensure all CTEs are
    421    moved to the top level so that the final SQL code is valid from a syntax standpoint.
    422
    423    TODO: handle name clashes whilst moving CTEs (it can get quite tricky & costly).
    424    """
    425    top_level_with = expression.args.get("with")
    426    for node in expression.find_all(exp.With):
    427        if node.parent is expression:
    428            continue
    429
    430        inner_with = node.pop()
    431        if not top_level_with:
    432            top_level_with = inner_with
    433            expression.set("with", top_level_with)
    434        else:
    435            if inner_with.recursive:
    436                top_level_with.set("recursive", True)
    437
    438            top_level_with.expressions.extend(inner_with.expressions)
    439
    440    return expression

Some dialects (e.g. Hive, T-SQL, Spark prior to version 3) only allow CTEs to be defined at the top-level, so for example queries like:

    SELECT * FROM (WITH t(c) AS (SELECT 1) SELECT * FROM t) AS subq

are invalid in those dialects. This transformation can be used to ensure all CTEs are moved to the top level so that the final SQL code is valid from a syntax standpoint.

TODO: handle name clashes whilst moving CTEs (it can get quite tricky & costly).

def ensure_bools( expression: sqlglot.expressions.Expression ) -> sqlglot.expressions.Expression: View Source

    443def ensure_bools(expression: exp.Expression) -> exp.Expression:
    444    """Converts numeric values used in conditions into explicit boolean expressions."""
    445    from sqlglot.optimizer.canonicalize import ensure_bools
    446
    447    def _ensure_bool(node: exp.Expression) -> None:
    448        if (
    449            node.is_number
    450            or node.is_type(exp.DataType.Type.UNKNOWN, *exp.DataType.NUMERIC_TYPES)
    451            or (isinstance(node, exp.Column) and not node.type)
    452        ):
    453            node.replace(node.neq(0))
    454
    455    for node, *_ in expression.walk():
    456        ensure_bools(node, _ensure_bool)
    457
    458    return expression

Converts numeric values used in conditions into explicit boolean expressions.

def unqualify_columns( expression: sqlglot.expressions.Expression ) -> sqlglot.expressions.Expression: View Source

    461def unqualify_columns(expression: exp.Expression) -> exp.Expression:
    462    for column in expression.find_all(exp.Column):
    463        # We only wanna pop off the table, db, catalog args
    464        for part in column.parts[:-1]:
    465            part.pop()
    466
    467    return expression

def preprocess( transforms: List[Callable[[ sqlglot.expressions.Expression ], sqlglot.expressions.Expression ]]) -> Callable[[ sqlglot.generator.Generator , sqlglot.expressions.Expression ], str]: View Source

    470def preprocess(
    471    transforms: t.List[t.Callable[[exp.Expression], exp.Expression]],
    472) -> t.Callable[[Generator, exp.Expression], str]:
    473    """
    474    Creates a new transform by chaining a sequence of transformations and converts the resulting
    475    expression to SQL, using either the "_sql" method corresponding to the resulting expression,
    476    or the appropriate `Generator.TRANSFORMS` function (when applicable -- see below).
    477
    478    Args:
    479        transforms: sequence of transform functions. These will be called in order.
    480
    481    Returns:
    482        Function that can be used as a generator transform.
    483    """
    484
    485    def _to_sql(self, expression: exp.Expression) -> str:
    486        expression_type = type(expression)
    487
    488        expression = transforms[0](expression)
    489        for transform in transforms[1:]:
    490            expression = transform(expression)
    491
    492        _sql_handler = getattr(self, expression.key + "_sql", None)
    493        if _sql_handler:
    494            return _sql_handler(expression)
    495
    496        transforms_handler = self.TRANSFORMS.get(type(expression))
    497        if transforms_handler:
    498            if expression_type is type(expression):
    499                if isinstance(expression, exp.Func):
    500                    return self.function_fallback_sql(expression)
    501
    502                # Ensures we don't enter an infinite loop. This can happen when the original expression
    503                # has the same type as the final expression and there's no _sql method available for it,
    504                # because then it'd re-enter _to_sql.
    505                raise ValueError(
    506                    f"Expression type {expression.__class__.__name__} requires a _sql method in order to be transformed."
    507                )
    508
    509            return transforms_handler(self, expression)
    510
    511        raise ValueError(f"Unsupported expression type {expression.__class__.__name__}.")
    512
    513    return _to_sql

Creates a new transform by chaining a sequence of transformations and converts the resulting expression to SQL, using either the "_sql" method corresponding to the resulting expression, or the appropriate `Generator.TRANSFORMS` function (when applicable -- see below).

###### Arguments:

- transforms: sequence of transform functions. These will be called in order.

###### Returns:

> Function that can be used as a generator transform.