Remove braces from regular expression result

Question

Problem

This code:

select
  x::text
from
  regexp_matches( 'i1 into o2, and g1 into o17', '[gio][0-9]{1,}', 'g' ) as x;

Returns these results:

{i1}
{o2}
{g1}
{o17}

Rather than the following results:

i1
o2
g1
o17

Related Links

• http://www.postgresql.org/docs/9.1/static/functions-matching.html

Question

What is the most efficient way to remove the braces using PostgreSQL 9.x?

Answer 1

Optimal Solution

Your regexp_matches() pattern can only result in a single element per pattern evaluation, so all resulting rows are constrained to exactly one array element. The expression simplifies to:

SELECT x[1]
FROM   regexp_matches('i1 into o2, and g1 into o17', '[gio][0-9]{1,}', 'g') AS x;

Other Solutions

SELECT unnest(x)  -- also works for cases with multiple elements per result row

SELECT trim(x::text, '{}') -- corner cases with results containing `{}`

SELECT rtrim(ltrim(x::text, '{'), '}') AS x1 -- fewer corner cases

If the pattern can or shall not match more than one time per input value, also drop the optional parameter 'g'.

And if the function shall always return exactly one row, consider the subtly different variant regexp_match() introduced with Postgres 10.

In Postgres 10 or later it's also prudent to suggest the set-returning function (SRF) regexp_matches() in the SELECT list directly (like Rick provided) since behavior of multiple SRFs in the SELECT list has finally been sanitized:

• What is the expected behaviour for multiple set-returning functions in select clause?