postgresql / sqlite / mysql /oracle regular expression operators

Migrated issue, originally created by Anonymous

match operator not implemented

in sqlalchemy/databases/postgres.py 727 just add sql_operators.match_op: lambda x, y, escape=None: ‘%s ~ %s’ % (x, y) + (escape and ’ ESCAPE '%s'’ % escape or ‘’),

and it works for me CAVEAT sql might crash if improper regexp syntax entered.

• missing imatch / notmatch …

(these matching functions are still used with same syntax) http://www.postgresql.org/docs/7.4/interactive/functions-matching.html

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Attachments: 1390.patch

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Edit 2020-07-10

Coping this recap from https://github.com/sqlalchemy/sqlalchemy/issues/5447#issue-654578670

The call column.regex_match('[a-z]*') would then evaluate to:

• Postgres: column ~ "[a-z]*"
• SQLite: column REGEXP "[a-z]*"
• MySQL, MariaDB: column REGEXP "[a-z]*"
• Oracle: REGEXP_LIKE(column, "[a-z]*")
• MSSQL: throw exception

[CaselIT]

Should we output the regex provided by the user verbatim, and warn them to use a portable subset of regex, or should we attempt to convert the regex to a backend-compatible version at execution time? (this sounds hard).

I think that a note on the documentation is enough in this case. It would be a lot of work to try and convert the regexp so I think that we should just render the input verbatim and let the db error if it is not correct

[multimeric]

Okay, here’s a feature matrix:

Feature	Postgres	MySQL	SQLite	Oracle	MSSQL
Does column match pattern?	column ~ pattern	column REGEXP pattern	column REGEXP pattern (requires plugin, but has syntax support)	REGEXP_LIKE(column, pattern)	n/a
Does column match pattern using flags?	column ~ (?flags)pattern	REGEXP_LIKE(column, pattern, flags)	n/a	REGEXP_LIKE(column, pattern, flags)	n/a
Replace pattern with replacement in column	regexp_replace(column, pattern, replacement)	REGEXP_REPLACE(column, pattern, replacement)	n/a (can be loaded as a custom function, but no syntax exists for this)	REGEXP_REPLACE(column, pattern, replacement)	n/a
Replace pattern with replacement in column with flags	regexp_replace(column, pattern, replacement , flags)	REGEXP_REPLACE(column, pattern, replacement, 1, 0, flags)	n/a	REGEXP_REPLACE(column, pattern, replacement)	n/a

Based on this, I think it makes sense to add the first row (“does column match regex”) as a core string-column function, but I’m undecided on the other two features. It would still be helpful to users to have them available in a database-independent manner, event though they are less well-supported.