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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().copy())
 71
 72        window = exp.alias_(window, row_number)
 73        expression.select(window, copy=False)
 74
 75        return exp.select(*outer_selects).from_(expression.subquery()).where(f'"{row_number}" = 1')
 76
 77    return expression
 78
 79
 80def eliminate_qualify(expression: exp.Expression) -> exp.Expression:
 81    """
 82    Convert SELECT statements that contain the QUALIFY clause into subqueries, filtered equivalently.
 83
 84    The idea behind this transformation can be seen in Snowflake's documentation for QUALIFY:
 85    https://docs.snowflake.com/en/sql-reference/constructs/qualify
 86
 87    Some dialects don't support window functions in the WHERE clause, so we need to include them as
 88    projections in the subquery, in order to refer to them in the outer filter using aliases. Also,
 89    if a column is referenced in the QUALIFY clause but is not selected, we need to include it too,
 90    otherwise we won't be able to refer to it in the outer query's WHERE clause.
 91    """
 92    if isinstance(expression, exp.Select) and expression.args.get("qualify"):
 93        taken = set(expression.named_selects)
 94        for select in expression.selects:
 95            if not select.alias_or_name:
 96                alias = find_new_name(taken, "_c")
 97                select.replace(exp.alias_(select, alias))
 98                taken.add(alias)
 99
100        outer_selects = exp.select(*[select.alias_or_name for select in expression.selects])
101        qualify_filters = expression.args["qualify"].pop().this
102
103        for expr in qualify_filters.find_all((exp.Window, exp.Column)):
104            if isinstance(expr, exp.Window):
105                alias = find_new_name(expression.named_selects, "_w")
106                expression.select(exp.alias_(expr, alias), copy=False)
107                column = exp.column(alias)
108
109                if isinstance(expr.parent, exp.Qualify):
110                    qualify_filters = column
111                else:
112                    expr.replace(column)
113            elif expr.name not in expression.named_selects:
114                expression.select(expr.copy(), copy=False)
115
116        return outer_selects.from_(expression.subquery(alias="_t")).where(qualify_filters)
117
118    return expression
119
120
121def remove_precision_parameterized_types(expression: exp.Expression) -> exp.Expression:
122    """
123    Some dialects only allow the precision for parameterized types to be defined in the DDL and not in
124    other expressions. This transforms removes the precision from parameterized types in expressions.
125    """
126    for node in expression.find_all(exp.DataType):
127        node.set("expressions", [e for e in node.expressions if isinstance(e, exp.DataType)])
128
129    return expression
130
131
132def unnest_to_explode(expression: exp.Expression) -> exp.Expression:
133    """Convert cross join unnest into lateral view explode (used in presto -> hive)."""
134    if isinstance(expression, exp.Select):
135        for join in expression.args.get("joins") or []:
136            unnest = join.this
137
138            if isinstance(unnest, exp.Unnest):
139                alias = unnest.args.get("alias")
140                udtf = exp.Posexplode if unnest.args.get("ordinality") else exp.Explode
141
142                expression.args["joins"].remove(join)
143
144                for e, column in zip(unnest.expressions, alias.columns if alias else []):
145                    expression.append(
146                        "laterals",
147                        exp.Lateral(
148                            this=udtf(this=e),
149                            view=True,
150                            alias=exp.TableAlias(this=alias.this, columns=[column]),  # type: ignore
151                        ),
152                    )
153
154    return expression
155
156
157def explode_to_unnest(expression: exp.Expression) -> exp.Expression:
158    """Convert explode/posexplode into unnest (used in hive -> presto)."""
159    if isinstance(expression, exp.Select):
160        from sqlglot.optimizer.scope import build_scope
161
162        scope = build_scope(expression)
163        if not scope:
164            return expression
165
166        taken_select_names = set(expression.named_selects)
167        taken_source_names = set(scope.selected_sources)
168
169        for select in expression.selects:
170            to_replace = select
171
172            pos_alias = ""
173            explode_alias = ""
174
175            if isinstance(select, exp.Alias):
176                explode_alias = select.alias
177                select = select.this
178            elif isinstance(select, exp.Aliases):
179                pos_alias = select.aliases[0].name
180                explode_alias = select.aliases[1].name
181                select = select.this
182
183            if isinstance(select, (exp.Explode, exp.Posexplode)):
184                is_posexplode = isinstance(select, exp.Posexplode)
185
186                explode_arg = select.this
187                unnest = exp.Unnest(expressions=[explode_arg.copy()], ordinality=is_posexplode)
188
189                # This ensures that we won't use [POS]EXPLODE's argument as a new selection
190                if isinstance(explode_arg, exp.Column):
191                    taken_select_names.add(explode_arg.output_name)
192
193                unnest_source_alias = find_new_name(taken_source_names, "_u")
194                taken_source_names.add(unnest_source_alias)
195
196                if not explode_alias:
197                    explode_alias = find_new_name(taken_select_names, "col")
198                    taken_select_names.add(explode_alias)
199
200                    if is_posexplode:
201                        pos_alias = find_new_name(taken_select_names, "pos")
202                        taken_select_names.add(pos_alias)
203
204                if is_posexplode:
205                    column_names = [explode_alias, pos_alias]
206                    to_replace.pop()
207                    expression.select(pos_alias, explode_alias, copy=False)
208                else:
209                    column_names = [explode_alias]
210                    to_replace.replace(exp.column(explode_alias))
211
212                unnest = exp.alias_(unnest, unnest_source_alias, table=column_names)
213
214                if not expression.args.get("from"):
215                    expression.from_(unnest, copy=False)
216                else:
217                    expression.join(unnest, join_type="CROSS", copy=False)
218
219    return expression
220
221
222def remove_target_from_merge(expression: exp.Expression) -> exp.Expression:
223    """Remove table refs from columns in when statements."""
224    if isinstance(expression, exp.Merge):
225        alias = expression.this.args.get("alias")
226        targets = {expression.this.this}
227        if alias:
228            targets.add(alias.this)
229
230        for when in expression.expressions:
231            when.transform(
232                lambda node: exp.column(node.name)
233                if isinstance(node, exp.Column) and node.args.get("table") in targets
234                else node,
235                copy=False,
236            )
237
238    return expression
239
240
241def remove_within_group_for_percentiles(expression: exp.Expression) -> exp.Expression:
242    if (
243        isinstance(expression, exp.WithinGroup)
244        and isinstance(expression.this, (exp.PercentileCont, exp.PercentileDisc))
245        and isinstance(expression.expression, exp.Order)
246    ):
247        quantile = expression.this.this
248        input_value = t.cast(exp.Ordered, expression.find(exp.Ordered)).this
249        return expression.replace(exp.ApproxQuantile(this=input_value, quantile=quantile))
250
251    return expression
252
253
254def add_recursive_cte_column_names(expression: exp.Expression) -> exp.Expression:
255    if isinstance(expression, exp.With) and expression.recursive:
256        next_name = name_sequence("_c_")
257
258        for cte in expression.expressions:
259            if not cte.args["alias"].columns:
260                query = cte.this
261                if isinstance(query, exp.Union):
262                    query = query.this
263
264                cte.args["alias"].set(
265                    "columns",
266                    [exp.to_identifier(s.alias_or_name or next_name()) for s in query.selects],
267                )
268
269    return expression
270
271
272def epoch_cast_to_ts(expression: exp.Expression) -> exp.Expression:
273    if (
274        isinstance(expression, (exp.Cast, exp.TryCast))
275        and expression.name.lower() == "epoch"
276        and expression.to.this in exp.DataType.TEMPORAL_TYPES
277    ):
278        expression.this.replace(exp.Literal.string("1970-01-01 00:00:00"))
279
280    return expression
281
282
283def preprocess(
284    transforms: t.List[t.Callable[[exp.Expression], exp.Expression]],
285) -> t.Callable[[Generator, exp.Expression], str]:
286    """
287    Creates a new transform by chaining a sequence of transformations and converts the resulting
288    expression to SQL, using either the "_sql" method corresponding to the resulting expression,
289    or the appropriate `Generator.TRANSFORMS` function (when applicable -- see below).
290
291    Args:
292        transforms: sequence of transform functions. These will be called in order.
293
294    Returns:
295        Function that can be used as a generator transform.
296    """
297
298    def _to_sql(self, expression: exp.Expression) -> str:
299        expression_type = type(expression)
300
301        expression = transforms[0](expression.copy())
302        for t in transforms[1:]:
303            expression = t(expression)
304
305        _sql_handler = getattr(self, expression.key + "_sql", None)
306        if _sql_handler:
307            return _sql_handler(expression)
308
309        transforms_handler = self.TRANSFORMS.get(type(expression))
310        if transforms_handler:
311            # Ensures we don't enter an infinite loop. This can happen when the original expression
312            # has the same type as the final expression and there's no _sql method available for it,
313            # because then it'd re-enter _to_sql.
314            if expression_type is type(expression):
315                raise ValueError(
316                    f"Expression type {expression.__class__.__name__} requires a _sql method in order to be transformed."
317                )
318
319            return transforms_handler(self, expression)
320
321        raise ValueError(f"Unsupported expression type {expression.__class__.__name__}.")
322
323    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().copy())
72
73        window = exp.alias_(window, row_number)
74        expression.select(window, copy=False)
75
76        return exp.select(*outer_selects).from_(expression.subquery()).where(f'"{row_number}" = 1')
77
78    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

 81def eliminate_qualify(expression: exp.Expression) -> exp.Expression:
 82    """
 83    Convert SELECT statements that contain the QUALIFY clause into subqueries, filtered equivalently.
 84
 85    The idea behind this transformation can be seen in Snowflake's documentation for QUALIFY:
 86    https://docs.snowflake.com/en/sql-reference/constructs/qualify
 87
 88    Some dialects don't support window functions in the WHERE clause, so we need to include them as
 89    projections in the subquery, in order to refer to them in the outer filter using aliases. Also,
 90    if a column is referenced in the QUALIFY clause but is not selected, we need to include it too,
 91    otherwise we won't be able to refer to it in the outer query's WHERE clause.
 92    """
 93    if isinstance(expression, exp.Select) and expression.args.get("qualify"):
 94        taken = set(expression.named_selects)
 95        for select in expression.selects:
 96            if not select.alias_or_name:
 97                alias = find_new_name(taken, "_c")
 98                select.replace(exp.alias_(select, alias))
 99                taken.add(alias)
100
101        outer_selects = exp.select(*[select.alias_or_name for select in expression.selects])
102        qualify_filters = expression.args["qualify"].pop().this
103
104        for expr in qualify_filters.find_all((exp.Window, exp.Column)):
105            if isinstance(expr, exp.Window):
106                alias = find_new_name(expression.named_selects, "_w")
107                expression.select(exp.alias_(expr, alias), copy=False)
108                column = exp.column(alias)
109
110                if isinstance(expr.parent, exp.Qualify):
111                    qualify_filters = column
112                else:
113                    expr.replace(column)
114            elif expr.name not in expression.named_selects:
115                expression.select(expr.copy(), copy=False)
116
117        return outer_selects.from_(expression.subquery(alias="_t")).where(qualify_filters)
118
119    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

122def remove_precision_parameterized_types(expression: exp.Expression) -> exp.Expression:
123    """
124    Some dialects only allow the precision for parameterized types to be defined in the DDL and not in
125    other expressions. This transforms removes the precision from parameterized types in expressions.
126    """
127    for node in expression.find_all(exp.DataType):
128        node.set("expressions", [e for e in node.expressions if isinstance(e, exp.DataType)])
129
130    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

133def unnest_to_explode(expression: exp.Expression) -> exp.Expression:
134    """Convert cross join unnest into lateral view explode (used in presto -> hive)."""
135    if isinstance(expression, exp.Select):
136        for join in expression.args.get("joins") or []:
137            unnest = join.this
138
139            if isinstance(unnest, exp.Unnest):
140                alias = unnest.args.get("alias")
141                udtf = exp.Posexplode if unnest.args.get("ordinality") else exp.Explode
142
143                expression.args["joins"].remove(join)
144
145                for e, column in zip(unnest.expressions, alias.columns if alias else []):
146                    expression.append(
147                        "laterals",
148                        exp.Lateral(
149                            this=udtf(this=e),
150                            view=True,
151                            alias=exp.TableAlias(this=alias.this, columns=[column]),  # type: ignore
152                        ),
153                    )
154
155    return expression

Convert cross join unnest into lateral view explode (used in presto -> hive).

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

158def explode_to_unnest(expression: exp.Expression) -> exp.Expression:
159    """Convert explode/posexplode into unnest (used in hive -> presto)."""
160    if isinstance(expression, exp.Select):
161        from sqlglot.optimizer.scope import build_scope
162
163        scope = build_scope(expression)
164        if not scope:
165            return expression
166
167        taken_select_names = set(expression.named_selects)
168        taken_source_names = set(scope.selected_sources)
169
170        for select in expression.selects:
171            to_replace = select
172
173            pos_alias = ""
174            explode_alias = ""
175
176            if isinstance(select, exp.Alias):
177                explode_alias = select.alias
178                select = select.this
179            elif isinstance(select, exp.Aliases):
180                pos_alias = select.aliases[0].name
181                explode_alias = select.aliases[1].name
182                select = select.this
183
184            if isinstance(select, (exp.Explode, exp.Posexplode)):
185                is_posexplode = isinstance(select, exp.Posexplode)
186
187                explode_arg = select.this
188                unnest = exp.Unnest(expressions=[explode_arg.copy()], ordinality=is_posexplode)
189
190                # This ensures that we won't use [POS]EXPLODE's argument as a new selection
191                if isinstance(explode_arg, exp.Column):
192                    taken_select_names.add(explode_arg.output_name)
193
194                unnest_source_alias = find_new_name(taken_source_names, "_u")
195                taken_source_names.add(unnest_source_alias)
196
197                if not explode_alias:
198                    explode_alias = find_new_name(taken_select_names, "col")
199                    taken_select_names.add(explode_alias)
200
201                    if is_posexplode:
202                        pos_alias = find_new_name(taken_select_names, "pos")
203                        taken_select_names.add(pos_alias)
204
205                if is_posexplode:
206                    column_names = [explode_alias, pos_alias]
207                    to_replace.pop()
208                    expression.select(pos_alias, explode_alias, copy=False)
209                else:
210                    column_names = [explode_alias]
211                    to_replace.replace(exp.column(explode_alias))
212
213                unnest = exp.alias_(unnest, unnest_source_alias, table=column_names)
214
215                if not expression.args.get("from"):
216                    expression.from_(unnest, copy=False)
217                else:
218                    expression.join(unnest, join_type="CROSS", copy=False)
219
220    return expression

Convert explode/posexplode into unnest (used in hive -> presto).

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

223def remove_target_from_merge(expression: exp.Expression) -> exp.Expression:
224    """Remove table refs from columns in when statements."""
225    if isinstance(expression, exp.Merge):
226        alias = expression.this.args.get("alias")
227        targets = {expression.this.this}
228        if alias:
229            targets.add(alias.this)
230
231        for when in expression.expressions:
232            when.transform(
233                lambda node: exp.column(node.name)
234                if isinstance(node, exp.Column) and node.args.get("table") in targets
235                else node,
236                copy=False,
237            )
238
239    return expression

Remove table refs from columns in when statements.

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

242def remove_within_group_for_percentiles(expression: exp.Expression) -> exp.Expression:
243    if (
244        isinstance(expression, exp.WithinGroup)
245        and isinstance(expression.this, (exp.PercentileCont, exp.PercentileDisc))
246        and isinstance(expression.expression, exp.Order)
247    ):
248        quantile = expression.this.this
249        input_value = t.cast(exp.Ordered, expression.find(exp.Ordered)).this
250        return expression.replace(exp.ApproxQuantile(this=input_value, quantile=quantile))
251
252    return expression

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

255def add_recursive_cte_column_names(expression: exp.Expression) -> exp.Expression:
256    if isinstance(expression, exp.With) and expression.recursive:
257        next_name = name_sequence("_c_")
258
259        for cte in expression.expressions:
260            if not cte.args["alias"].columns:
261                query = cte.this
262                if isinstance(query, exp.Union):
263                    query = query.this
264
265                cte.args["alias"].set(
266                    "columns",
267                    [exp.to_identifier(s.alias_or_name or next_name()) for s in query.selects],
268                )
269
270    return expression

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

273def epoch_cast_to_ts(expression: exp.Expression) -> exp.Expression:
274    if (
275        isinstance(expression, (exp.Cast, exp.TryCast))
276        and expression.name.lower() == "epoch"
277        and expression.to.this in exp.DataType.TEMPORAL_TYPES
278    ):
279        expression.this.replace(exp.Literal.string("1970-01-01 00:00:00"))
280
281    return expression

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

284def preprocess(
285    transforms: t.List[t.Callable[[exp.Expression], exp.Expression]],
286) -> t.Callable[[Generator, exp.Expression], str]:
287    """
288    Creates a new transform by chaining a sequence of transformations and converts the resulting
289    expression to SQL, using either the "_sql" method corresponding to the resulting expression,
290    or the appropriate `Generator.TRANSFORMS` function (when applicable -- see below).
291
292    Args:
293        transforms: sequence of transform functions. These will be called in order.
294
295    Returns:
296        Function that can be used as a generator transform.
297    """
298
299    def _to_sql(self, expression: exp.Expression) -> str:
300        expression_type = type(expression)
301
302        expression = transforms[0](expression.copy())
303        for t in transforms[1:]:
304            expression = t(expression)
305
306        _sql_handler = getattr(self, expression.key + "_sql", None)
307        if _sql_handler:
308            return _sql_handler(expression)
309
310        transforms_handler = self.TRANSFORMS.get(type(expression))
311        if transforms_handler:
312            # Ensures we don't enter an infinite loop. This can happen when the original expression
313            # has the same type as the final expression and there's no _sql method available for it,
314            # because then it'd re-enter _to_sql.
315            if expression_type is type(expression):
316                raise ValueError(
317                    f"Expression type {expression.__class__.__name__} requires a _sql method in order to be transformed."
318                )
319
320            return transforms_handler(self, expression)
321
322        raise ValueError(f"Unsupported expression type {expression.__class__.__name__}.")
323
324    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.