String matching in PostgreSQL 8.4

问题

I need to implement a regular expression (as I understand) matching in PostgreSQL 8.4. It seems regular expression matching are only available in 9.0+.

My need is:

When I give an input 14.1 I need to get these results:

14.1.1
14.1.2
14.1.Z
...

But exclude:

14.1.1.1
14.1.1.K
14.1.Z.3.A
...

The pattern is not limited to a single character. There is always a possibility that a pattern like this will be presented: 14.1.1.2K, 14.1.Z.13.A2 etc., because the pattern is provided the user. The application has no control over the pattern (it's not a version number).

Any idea how to implement this in Postgres 8.4?

After one more question my issue was solved Escaping a LIKE pattern or regexp string in Postgres 8.4 inside a stored procedure

回答1:

First of all, regular expression matching has been in Postgres practically for ever, at least since version 7.1. Use the these operators:

~ !~ ~* !~*

Overview on dba.SE:

Pattern matching with LIKE, SIMILAR TO or regular expressions in PostgreSQL

The point in your case seems to be, that another dot is not allowed:

SELECT *
FROM   tbl
WHERE  version LIKE '14.1.%'        -- for performance
AND    version ~ '^14\.1\.[^.]+$';  -- for correct result

SQL Fiddle.

The LIKE expression is redundant, but it is going to improve performance dramatically, even without index. But you should have an index, of course.

The LIKE expression can use a basic text_pattern_ops index, while the regular expression cannot, at least in Postgres 8.4.

PostgreSQL LIKE query performance variations

[^.] in the regex pattern is a character class that excludes the dot (.). So any other character is allowed, just no more dots.

Performance

To squeeze out top performance for this particular query you could add a specialized index:

CREATE INDEX tbl_specail_idx ON tbl
((length(version) - length(replace(version, '.', ''))), version text_pattern_ops);

And use a matching query, the same as above, just replace the last line with:

AND   length(version) - length(replace(version, '.', '')) = 2

SQL Fiddle.

回答2:

You can't do regex matching, but I believe you can do like operators so:

SELECT * FROM table WHERE version LIKE '14.1._';

Will match any row with a version of '14.1.' followed by a single character. This should match your examples. Note that this will not match just '14.1', if you needed this as well. You could do this with an OR.

SELECT * FROM table WHERE version LIKE '14.1._' OR version = '14.1';

回答3:

Regex matching should be possible with Postgresql-8.4 like this:

SELECT * FROM table WHERE version ~ '^14\.1\..$';

来源：https://stackoverflow.com/questions/29407320/string-matching-in-postgresql-8-4

标签

regex

postgresql

postgresql-8.4