sqlglot/sqlglot/dialects/__init__.py

"""
## Dialects

While there is a SQL standard, most SQL engines support a variation of that standard. This makes it difficult
to write portable SQL code. SQLGlot bridges all the different variations, called "dialects", with an extensible
SQL transpilation framework. 

The base `sqlglot.dialects.dialect.Dialect` class implements a generic dialect that aims to be as universal as possible.

Each SQL variation has its own `Dialect` subclass, extending the corresponding `Tokenizer`, `Parser` and `Generator`
classes as needed.

### Implementing a custom Dialect

Consider the following example:

```python
from sqlglot import exp
from sqlglot.dialects.dialect import Dialect
from sqlglot.generator import Generator
from sqlglot.tokens import Tokenizer, TokenType


class Custom(Dialect):
    class Tokenizer(Tokenizer):
        QUOTES = ["'", '"']
        IDENTIFIERS = ["`"]

        KEYWORDS = {
            **Tokenizer.KEYWORDS,
            "INT64": TokenType.BIGINT,
            "FLOAT64": TokenType.DOUBLE,
        }

    class Generator(Generator):
        TRANSFORMS = {exp.Array: lambda self, e: f"[{self.expressions(e)}]"}

        TYPE_MAPPING = {
            exp.DataType.Type.TINYINT: "INT64",
            exp.DataType.Type.SMALLINT: "INT64",
            exp.DataType.Type.INT: "INT64",
            exp.DataType.Type.BIGINT: "INT64",
            exp.DataType.Type.DECIMAL: "NUMERIC",
            exp.DataType.Type.FLOAT: "FLOAT64",
            exp.DataType.Type.DOUBLE: "FLOAT64",
            exp.DataType.Type.BOOLEAN: "BOOL",
            exp.DataType.Type.TEXT: "STRING",
        }
```

This is a typical example of adding a new dialect implementation in SQLGlot: we specify its identifier and string
delimiters, as well as what tokens it uses for its types and how they're associated with SQLGlot types. Since
the `Expression` classes are common for each dialect supported in SQLGlot, we may also need to override the generation
logic for some expressions; this is usually done by adding new entries to the `TRANSFORMS` mapping.

----
"""

from sqlglot.dialects.bigquery import BigQuery
from sqlglot.dialects.clickhouse import ClickHouse
from sqlglot.dialects.databricks import Databricks
from sqlglot.dialects.dialect import Dialect, Dialects
from sqlglot.dialects.doris import Doris
from sqlglot.dialects.drill import Drill
from sqlglot.dialects.duckdb import DuckDB
from sqlglot.dialects.hive import Hive
from sqlglot.dialects.mysql import MySQL
from sqlglot.dialects.oracle import Oracle
from sqlglot.dialects.postgres import Postgres
from sqlglot.dialects.presto import Presto
from sqlglot.dialects.redshift import Redshift
from sqlglot.dialects.snowflake import Snowflake
from sqlglot.dialects.spark import Spark
from sqlglot.dialects.spark2 import Spark2
from sqlglot.dialects.sqlite import SQLite
from sqlglot.dialects.starrocks import StarRocks
from sqlglot.dialects.tableau import Tableau
from sqlglot.dialects.teradata import Teradata
from sqlglot.dialects.trino import Trino
from sqlglot.dialects.tsql import TSQL