An easily customizable SQL parser and transpiler
Project description
SQLGlot
SQLGlot is a no dependency Python SQL parser and transpiler. It can be used to format SQL or translate between different dialects like Presto, Spark, and SQLite. It aims to read a wide variety of SQL inputs and output syntatically correct SQL in the targeted dialects.
This project is actively in development and alpha level quality.
You can easily customize the parser to support UDF's across dialects as well through the transform API.
Syntax errors are highlighted and dialect incompatibilities can warn or raise depending on configurations.
Examples
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`
Custom Transforms
A simple transform on types can be accomplished by providing a dict of Expression/TokenType => lambda/string
from sqlglot import *
transpile("SELECT CAST(a AS INT) FROM x", transforms={TokenType.INT: 'SPECIAL INT'})[0]
SELECT CAST(a AS SPECIAL INT) FROM x
More complicated transforms can be accomplished by using the Tokenizer, Parser, and Generator directly.
In this example, we want to parse a UDF SPECIAL_UDF and then output another version called SPECIAL_UDF_INVERSE with the arguments switched.
from sqlglot import *
from sqlglot.expressions import Func
class SpecialUDF(Func):
arg_types = {'a': True, 'b': True}
tokens = Tokenizer().tokenize("SELECT SPECIAL_UDF(a, b) FROM x")
Here is the output of the tokenizer.
[
<Token token_type: TokenType.SELECT, text: SELECT, line: 0, col: 0>,
<Token token_type: TokenType.VAR, text: SPECIAL_UDF, line: 0, col: 7>,
<Token token_type: TokenType.L_PAREN, text: (, line: 0, col: 18>,
<Token token_type: TokenType.VAR, text: a, line: 0, col: 19>,
<Token token_type: TokenType.COMMA, text: ,, line: 0, col: 20>,
<Token token_type: TokenType.VAR, text: b, line: 0, col: 22>,
<Token token_type: TokenType.R_PAREN, text: ), line: 0, col: 23>,
<Token token_type: TokenType.FROM, text: FROM, line: 0, col: 25>,
<Token token_type: TokenType.VAR, text: x, line: 0, col: 30>,
]
expression = Parser(functions={
'SPECIAL_UDF': lambda args: SpecialUDF(a=args[0], b=args[1]),
}).parse(tokens)[0]
The expression tree produced by the parser.
(FROM this:
(TABLE this: x, db: ), expression:
(SELECT expressions:
(COLUMN this:
(FUNC a:
(COLUMN this: a, db: , table: ), b:
(COLUMN this: b, db: , table: )), db: , table: )))
Finally generating the new SQL.
Generator(transforms={
SpecialUDF: lambda self, e: f"SPECIAL_UDF_INVERSE({self.sql(e, 'b')}, {self.sql(e, 'a')})"
}).generate(expression)
SELECT SPECIAL_UDF_INVERSE(b, a) FROM x
Parse Errors
A syntax error will result in an parse error.
transpile("SELECT foo( FROM bar")
sqlglot.errors.ParseError: Expected )
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
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