Home/ Questions/Q 8788659
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-06-13T22:11:42+00:00

I need to retrieve certain rows from a table depending on certain values in

  • 0

I need to retrieve certain rows from a table depending on certain values in a specific column, named columnX in the example:

select *
from tableName 
where columnX similar to ('%A%|%B%|%C%|%1%|%2%|%3%')

So if columnX contains at least one of the values specified (A, B, C, 1, 2, 3), I will keep the row.

I can’t find a better approach than using similar to. The problem is that the query takes too long for a table with more than a million rows.

I’ve tried indexing it:

create index tableName_columnX_idx on tableName (columnX) 
where columnX similar to ('%A%|%B%|%C%|%1%|%2%|%3%')

However, if the condition is variable (the values could be other than A, B, C, 1, 2, 3), I would need a different index for each condition.

Is there any better solution for this problem?

EDIT: Thanks everybody for the feedback. Looks like I’ve achieved to this point maybe because of a design mistake (topic I’ve posted in a separated question).

Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Editorial Team

    I agree with Quassnoi, a GIN index is fastest and simplest – unless write performance or disk space are issues, because it occupies a lot of space and adds cost for INSERT, UPDATE and DELETE.

    My additional answer is triggered by your statement:

    I can’t find a better approach than using similar to.

    If that is what you found, then your search isn’t over, yet. SIMILAR TO is a complete waste of time. Literally. Postgres only includes it to comply to the (weird) SQL standard. Inspect the output of EXPLAIN ANALYZE for your query and you will find that SIMILAR TO has been replaced by a regular expression.

    Internally every SIMILAR TO expression is rewritten to a regular expression. Consequently, for each and every SIMILAR TO expression there is at least one regular expression match that is a bit faster. Let EXPLAIN ANALYZE translate it for you, if you are not sure. You won’t find this in the manual, PostgreSQL does not promise to do it this way, but I have yet to see an exception.

    Further reading:

    • 0