Question

Very short question. Can anyone say why this query

select LENGTH(' '::char || ' '::char), LENGTH(' '::text || ' '::char), LENGTH(' ' || ' '), LENGTH('a'::char || 'b'::char);

returns

0    1    2    2

Is space a special character witch don’t concatenate with other strings?

Documentation says only this:

Unless otherwise noted, all of the functions listed below work
on all of these types, but be wary of potential effects of
automatic space-padding when using the character type.

Why I do this? Because i’m building string char by char in stored procedure, and when i try to concatenate varchar with char nothing happens.

Answer 1

The CHAR type is “fixed-length, blank padded”. This means that if you store "foobar" into a char(10) field, Postgres actually stores "foobar " (that’s four trailing spaces, SO does not preserve adjacent whitespace). When you fetch back your value, any trailing whitespace is stripped out. The same happens with ' '::char — its trailing whitespace is stripped, leaving only a zero-length string.