hcq/postgresql
1
0
Fork 0
mirror of https://git.postgresql.org/git/postgresql.git synced 2026-02-22 22:37:01 +08:00
Code Issues Packages Projects Releases Wiki Activity

Fix issues around strictness of SIMILAR TO.

Browse Source 
As a result of some long-ago quick hacks, the SIMILAR TO operator
and the corresponding flavor of substring() interpreted "ESCAPE NULL"
as selecting the default escape character '\'.  This is both
surprising and not per spec: the standard is clear that these
functions should return NULL for NULL input.

Additionally, because of inconsistency of the strictness markings
of 3-argument substring() and similar_escape(), the planner could not
inline the SQL definition of substring(), resulting in a substantial
performance penalty compared to the underlying POSIX substring()
function.

The simplest fix for this would be to change the strictness marking
of similar_escape(), but if we do that we risk breaking existing views
that depend on that function.  Hence, leave similar_escape() as-is
as a compatibility function, and instead invent a new function
similar_to_escape() that comes in two strict variants.

There are a couple of other behaviors in this area that are also
not per spec, but they are documented and seem generally at least
as sane as the spec's definition, so leave them alone.  But improve
the documentation to describe them fully.

Patch by me; thanks to Álvaro Herrera and Andrew Gierth for review
and discussion.

Discussion: https://postgr.es/m/14047.1557708214@sss.pgh.pa.us
This commit is contained in:
Tom Lane
2019-09-07 14:21:59 -04:00
parent c5bc7050af
commit ca70bdaefe
7 changed files with 193 additions and 41 deletions
Download Patch File Download Diff File Expand all files Collapse all files

15
src/test/regress/sql/strings.sql
View File

@ -144,7 +144,20 @@ SELECT SUBSTRING('abcdefg' FROM 'c.e') AS "cde";
-- With a parenthesized subexpression, return only what matches the subexpr
SELECT SUBSTRING('abcdefg' FROM 'b(.*)f') AS "cde";
-- PostgreSQL extension to allow using back reference in replace string;
-- Check behavior of SIMILAR TO, which uses largely the same regexp variant
SELECT 'abcdefg' SIMILAR TO '_bcd%' AS true;
SELECT 'abcdefg' SIMILAR TO 'bcd%' AS false;
SELECT 'abcdefg' SIMILAR TO '_bcd#%' ESCAPE '#' AS false;
SELECT 'abcd%' SIMILAR TO '_bcd#%' ESCAPE '#' AS true;
-- Postgres uses '\' as the default escape character, which is not per spec
SELECT 'abcdefg' SIMILAR TO '_bcd\%' AS false;
-- and an empty string to mean "no escape", which is also not per spec
SELECT 'abcd\efg' SIMILAR TO '_bcd\%' ESCAPE '' AS true;
-- these behaviors are per spec, though:
SELECT 'abcdefg' SIMILAR TO '_bcd%' ESCAPE NULL AS null;
SELECT 'abcdefg' SIMILAR TO '_bcd#%' ESCAPE '##' AS error;
-- Test back reference in regexp_replace
SELECT regexp_replace('1112223333', E'(\\d{3})(\\d{3})(\\d{4})', E'(\\1) \\2-\\3');
SELECT regexp_replace('AAA BBB CCC ', E'\\s+', ' ', 'g');
SELECT regexp_replace('AAA', '^|$', 'Z', 'g');