Re: EXISTS

Denis Woodbury wrote:
> Hi,
>
> I would like to know if this this type of statement can be used in
> Postgresql
>
> IF NOT EXISTS (SELECT 1 FROM Table WHERE col1 = 'mystring' )
> BEGIN
> ...
> END

PostgreSQL doesn't have any sort of free block flow control; it doesn't
have an IF statement or similar in SQL. You can usually just create a
PL/PgSQL function to do what you want.

It'd occasionally be nice to be able to write PL/PgSQL bodies in-line in
SQL code rather than explicitly creating then dropping a function when
you do need to do something a bit weird (usually in admin/maintenance
scripts) but the current approach does work fine.

It also helps that you can often achieve the required logic with plain,
standard SQL. The CASE statement is particularly useful:

SELECT
CASE
WHEN col1 = 'mystring' THEN [expression or function call]
END
FROM Table;

--
Craig Ringer