rolandwalker / sqlglot

Python SQL Parser and Transpiler

SQLGlot

SQLGlot is a no dependency Python SQL parser, transpiler, and optimizer. It can be used to format SQL or translate between different dialects like DuckDB, Presto, Spark, and BigQuery. It aims to read a wide variety of SQL inputs and output syntactically correct SQL in the targeted dialects.

It is a very comprehensive generic SQL parser with a robust test suite. It is also quite performant while being written purely in Python.

You can easily customize the parser, analyze queries, traverse expression trees, and programmatically build SQL.

Syntax errors are highlighted and dialect incompatibilities can warn or raise depending on configurations.

Install

From PyPI

pip3 install sqlglot

Or with a local checkout

pip3 install -e .

Examples

Easily translate from one dialect to another. For example, date/time functions vary from dialects and can be hard to deal with.

import sqlglot
sqlglot.transpile("SELECT EPOCH_MS(1618088028295)", read='duckdb', write='hive')

SELECT TO_UTC_TIMESTAMP(FROM_UNIXTIME(1618088028295 / 1000, 'yyyy-MM-dd HH:mm:ss'), 'UTC')

SQLGlot can even translate custom time formats.

import sqlglot
sqlglot.transpile("SELECT STRFTIME(x, '%y-%-m-%S')", read='duckdb', write='hive')

SELECT DATE_FORMAT(x, 'yy-M-ss')"

Formatting and Transpiling

Read in a SQL statement with a CTE and CASTING to a REAL and then transpiling to Spark.

Spark uses backticks as identifiers and the REAL type is transpiled to FLOAT.

import sqlglot

sql = """WITH baz AS (SELECT a, c FROM foo WHERE a = 1) SELECT f.a, b.b, baz.c, CAST("b"."a" AS REAL) d FROM foo f JOIN bar b ON f.a = b.a LEFT JOIN baz ON f.a = baz.a"""
sqlglot.transpile(sql, write='spark', identify=True, pretty=True)[0]

WITH `baz` AS (
  SELECT
    `a`,
    `c`
  FROM `foo`
  WHERE
    `a` = 1
)
SELECT
  `f`.`a`,
  `b`.`b`,
  `baz`.`c`,
  CAST(`b`.`a` AS FLOAT) AS `d`
FROM `foo` AS `f`
JOIN `bar` AS `b`
  ON `f`.`a` = `b`.`a`
LEFT JOIN `baz`
  ON `f`.`a` = `baz`.`a`

Metadata

You can explore SQL with expression helpers to do things like find columns and tables.

from sqlglot import parse_one, exp

# print all column references (a and b)
for column in parse_one("SELECT a, b + 1 AS c FROM d").find_all(exp.Column):
  print(column.alias_or_name)

# find all projections in select statements (a and c)
for select in parse_one("SELECT a, b + 1 AS c FROM d").find_all(exp.Select):
  for projection in select.expressions:
    print(projection.alias_or_name)

# find all tables (x, y, z)
for table in parse_one("SELECT * FROM x JOIN y JOIN z").find_all(exp.Table):
  print(table.name)

Parser Errors

A syntax error will result in a parser error.

transpile("SELECT foo( FROM bar")

sqlglot.errors.ParseError: Expecting ). Line 1, Col: 13. select foo( FROM bar

Unsupported Errors

Presto APPROX_DISTINCT supports the accuracy argument which is not supported in Spark.

transpile(
    'SELECT APPROX_DISTINCT(a, 0.1) FROM foo',
    read='presto',
    write='spark',
)

WARNING:root:APPROX_COUNT_DISTINCT does not support accuracy

SELECT APPROX_COUNT_DISTINCT(a) FROM foo

Build and Modify SQL

SQLGlot supports incrementally building sql expressions.

from sqlglot import select, condition

where = condition("x=1").and_("y=1")
select("*").from_("y").where(where).sql()

Which outputs:

SELECT * FROM y WHERE x = 1 AND y = 1

You can also modify a parsed tree:

from sqlglot import parse_one

parse_one("SELECT x FROM y").from_("z").sql()

Which outputs:

SELECT x FROM y, z

There is also a way to recursively transform the parsed tree by applying a mapping function to each tree node:

from sqlglot import exp, parse_one

expression_tree = parse_one("SELECT a FROM x")

def transformer(node):
    if isinstance(node, exp.Column) and node.name == "a":
        return parse_one("FUN(a)")
    return node

transformed_tree = expression_tree.transform(transformer)
transformed_tree.sql()

Which outputs:

SELECT FUN(a) FROM x

SQL Optimizer

SQLGlot can rewrite queries into an "optimized" form. It performs a variety of techniques to create a new canonical AST. This AST can be used to standardize queries or provide the foundations for implementing an actual engine.

import sqlglot
from sqlglot.optimizer import optimize

>>>
optimize(
    sqlglot.parse_one("""
    SELECT A OR (B OR (C AND D))
    FROM x
    WHERE Z = date '2021-01-01' + INTERVAL '1' month OR 1 = 0
    """),
    schema={"x": {"A": "INT", "B": "INT", "C": "INT", "D": "INT", "Z": "STRING"}}
).sql(pretty=True)

"""
SELECT
  (
    "x"."A"
    OR "x"."B"
    OR "x"."C"
  )
  AND (
    "x"."A"
    OR "x"."B"
    OR "x"."D"
  ) AS "_col_0"
FROM "x" AS "x"
WHERE
  "x"."Z" = CAST('2021-02-01' AS DATE)
"""

SQL Annotations

SQLGlot supports annotations in the sql expression. This is an experimental feature that is not part of any of the SQL standards but it can be useful when needing to annotate what a selected field is supposed to be. Below is an example:

SELECT
  user #primary_key,
  country
FROM users

AST Introspection

You can see the AST version of the sql by calling repr.

from sqlglot import parse_one
repr(parse_one("SELECT a + 1 AS z"))

(SELECT expressions:
  (ALIAS this:
    (ADD this:
      (COLUMN this:
        (IDENTIFIER this: a, quoted: False)), expression:
      (LITERAL this: 1, is_string: False)), alias:
    (IDENTIFIER this: z, quoted: False)))

AST Diff

SQLGlot can calculate the difference between two expressions and output changes in a form of a sequence of actions needed to transform a source expression into a target one.

from sqlglot import diff, parse_one
diff(parse_one("SELECT a + b, c, d"), parse_one("SELECT c, a - b, d"))

[
  Remove(expression=(ADD this:
    (COLUMN this:
      (IDENTIFIER this: a, quoted: False)), expression:
    (COLUMN this:
      (IDENTIFIER this: b, quoted: False)))),
  Insert(expression=(SUB this:
    (COLUMN this:
      (IDENTIFIER this: a, quoted: False)), expression:
    (COLUMN this:
      (IDENTIFIER this: b, quoted: False)))),
  Move(expression=(COLUMN this:
    (IDENTIFIER this: c, quoted: False))),
  Keep(source=(IDENTIFIER this: b, quoted: False), target=(IDENTIFIER this: b, quoted: False)),
  ...
]

Custom Dialects

Dialects can be added by subclassing Dialect.

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


class Custom(Dialect):
    identifier = "`"

    class Tokenizer(Tokenizer):
        QUOTES = ["'", '"']

        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",
        }


Dialects["custom"]

Benchmarks

Benchmarks run on Python 3.10.5 in seconds.

Query	sqlglot	sqltree	sqlparse	moz_sql_parser	sqloxide
tpch	0.01178 (1.0)	0.01173 (0.995)	0.04676 (3.966)	0.06800 (5.768)	0.00094 (0.080)
short	0.00084 (1.0)	0.00079 (0.948)	0.00296 (3.524)	0.00443 (5.266)	0.00006 (0.072)
long	0.01102 (1.0)	0.01044 (0.947)	0.04349 (3.945)	0.05998 (5.440)	0.00084 (0.077)
crazy	0.03751 (1.0)	0.03471 (0.925)	11.0796 (295.3)	1.03355 (27.55)	0.00529 (0.141)

Run Tests and Lint

pip install -r requirements.txt
./format_code.sh
./run_checks.sh

Optional Dependencies

SQLGlot uses dateutil to simplify literal timedelta expressions. The optimizer will not simplify expressions like

x + interval '1' month

if the module cannot be found.