Monday, July 24. 2006
Reverse a text in PostgreSQL
Andreas 'ads' Scherbaum
I'm always searching for a reverse function, so here is the link:
http://www.varlena.com/GeneralBits/53.php
code snippet is available in plperl and plpgsql.
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Using recursion, one can also achieve it with a plain sql function:
create function reverse(text) returns text as $$
select case when length($1)>0
then substring($1, length($1), 1) || reverse(substring($1, 1, length($1)-1))
else '' end $$ language sql immutable strict;
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a code from Varlena is not good - there is a few issues - first issue is using a WHILE statement. FOR statement is better - is faster. And you can use a simple and relative fast SQL function
create or replace function rvrs(text)
returns text as $$
select string_agg(substring($1 from i for 1),'')
from generate_series(length($1),1,-1) g(i)
$$ language sql;
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Here is one more function to reverse text that uses FOR statement if anybody interested.
create or replace function rev(varchar) returns varchar as $$
declare
_temp varchar;
_count int;
begin
_temp := '';
for _count in reverse length($1)..1 loop
_temp := _temp || substring($1 from _count for 1);
end loop;
return _temp;
end;
$$ language plpgsql immutable;
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