Support LIKE pattern without any escape character #13291
Description
Is your feature request related to a problem or challenge?
in standard SQL, as well as in a few systems LIKE pattern without explicit ESCAPE has no implicit ESCAPE character. Or at (least it's not a backslash)
Some systems WITHOUT implicit \ escape in LIKE patterns
Oracle 23c
If esc_char is not specified, then there is no default escape character.
I couldn't confirm this with db-fiddle. I think it's processing \% incorrectly on query input or output
Trino 461
SELECT
-- verify backslash treatment in a string literal
'\a' AS backslash_a,
'\%' AS backslash_percent,
-- verify backslash treatment in a LIKE pattern without explicit «ESCAPE '\'» clause
'a' LIKE '\%' AS a,
'\a' LIKE '\%' AS b,
'%' LIKE '\%' AS c,
'\%' LIKE '\%' AS d backslash_a | backslash_percent | a | b | c | d
-------------+-------------------+-------+------+-------+------
\a | \% | false | true | false | true
SQL Server
SELECT a,
CASE WHEN
(a LIKE '\%') OR NOT (a LIKE '\%')
THEN CASE WHEN (a LIKE '\%') THEN 'true' ELSE 'false' END
ELSE 'NULL'
END AS is_like
FROM (VALUES ('a'), ('\a'), ('%'), ('\%')) t(a)a | is_like
-- | --
a | false
\a | true
% | false
\% | true
Snowflake
-- using $$-quoted strings to avoid need to scape the backslash
SELECT
-- verify backslash treatment in a string literal
$$\a$$ AS backslash_a,
$$\%$$ AS backslash_percent,
-- verify backslash treatment in a LIKE pattern without explicit «ESCAPE $$\$$» clause
$$a$$ LIKE $$\%$$ AS a,
$$\a$$ LIKE $$\%$$ AS b,
$$%$$ LIKE $$\%$$ AS c,
$$\%$$ LIKE $$\%$$ AS dBACKSLASH_A | BACKSLASH_PERCENT | A | B | C | D
-- | -- | -- | -- | -- | --
\a | \% | FALSE | TRUE | FALSE | TRUE
(note: not using GitHub markdown table rendering, as it renders \% in cells as %)
Some systems WITH implicit \ escape in LIKE patterns
PostgreSQL 17
postgres=# select version();
version
---------------------------------------------------------------------------------------------------------------------------
PostgreSQL 17.0 (Debian 17.0-1.pgdg120+1) on aarch64-unknown-linux-gnu, compiled by gcc (Debian 12.2.0-14) 12.2.0, 64-bit
(1 row)
postgres=# SELECT
-- verify backslash treatment in a string literal
'\a' AS backslash_a,
'\%' AS backslash_percent,
-- verify backslash treatment in a LIKE pattern without explicit «ESCAPE '\'» clause
'a' LIKE '\%' AS a,
'\a' LIKE '\%' AS b,
'%' LIKE '\%' AS c,
'\%' LIKE '\%' AS d;
backslash_a | backslash_percent | a | b | c | d
-------------+-------------------+---+---+---+---
\a | \% | f | f | t | f
DataFusion
not showing CLI output due to #13286
SLT test is like this (copied from #13288)
# \ is an implicit escape character
query BBBB
SELECT
'a' LIKE '\%',
'\a' LIKE '\%',
'%' LIKE '\%',
'\%' LIKE '\%'
----
false false true false
# \ is an implicit escape character
query BBBBBB
SELECT
'a' LIKE '\_',
'\a' LIKE '\_',
'_' LIKE '\_',
'\_' LIKE '\_',
'abc' LIKE 'a_c',
'abc' LIKE 'a\_c'
----
false false true false true false
Describe the solution you'd like
I'd like DataFusion to follow SQL standard.
LIKE without an ESCAPE should behave as not having an escape character.
LIKE with ESCAPE '\' should behave as having \ escape character.
Describe alternatives you've considered
Picking arbitrary escape character to represent LIKE without an ESCAPE.
This works for static patterns, as the pattern can be verified not to contain the escape character chosen.
This does not work however for patterns being dynamic.