Tuesday 10 August 2010

How to convert an array to a table?

This little function can explode array item into a table item

CREATE OR REPLACE FUNCTION explode_array(in_array anyarray)
RETURNS SETOF anyelement AS
$BODY$
select ($1)[s] from generate_series(1,array_upper($1, 1)) as s;
$BODY$
LANGUAGE 'sql' IMMUTABLE
COST 100
ROWS 1000;


Example use:

=> select explode_array(array[1,2,3]);
explode_array
---------------
1
2
3
(3 rows)

ALTER TABLE ADD COLUMN IF NOT EXISTS OR ADD COLUMN WITH incremental suffix IF EXISTS

A generic way to add a new column in PostgreSQL 8.3 from plpgsql by incrementing column suffix in a case when column already exists.

DECLARE
query TEXT :='';
suffix INTEGER :=0;
recs INTEGER :=0;
BEGIN

LOOP
suffix = suffix + 1;
EXECUTE 'SELECT count(*) FROM information_schema.columns
WHERE table_schema||$$.$$||table_name = $$'||mytablename||'$$
AND column_name = $$mycolumn'||suffix||'$$' INTO recs;
RAISE INFO 'recs %!', recs;
IF recs = 0 THEN
EXECUTE 'ALTER TABLE '||tablename||' ADD COLUMN class'||suffix||' INTEGER';
RAISE INFO 'Column mycolumn% was added!', suffix;
EXIT;
END IF;
END LOOP;