Question

Short version: I need a function to escape strings for use in LIKE expressions, so fr_e%d becomes fr\_e\%d.

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I’m looking for escape the result of a query without the need to use replace.
Because in this result I have path with this char _ inside. And because I use this result in a LIKE statement, it make the “_” a joker like start *.

I have to use LIKE because I’m doing some stuff concatenation in this same statement who need the fact that I use LIKE.

I tried ~ to replace LIKE but I will have the same problem with the char ‘.’ because ~ is to use regex just skip this solution too.

Answer 1

create function quote_like(text) returns text language sql immutable strict as
  $quote_like$
    select regexp_replace($1, $$[_%\\]$$, $$\\\&$$, 'g');
  $quote_like$;

This function prepends all occurrences of _, % and \ in provided string with \. You can use it for example like this:

select * from tablename
  where tablecolumn like
    '%'
    ||
    (select quote_like(substring) from substrings where substring_id=123)
    ||
    '%';