How to select an empty result set?
SqlMysqlStored ProceduresNullResultsetSql Problem Overview
I'm using a stored procedure in MySQL, with a CASE statement.
In the ELSE clause of the CASE ( equivalent to default: ) I want to select and return an empty result set, thus avoiding to throw an SQL error by not handling the ELSE case, and instead return an empty result set as if a regular query would have returned no rows.
So far I've managed to do so using something like:
Select NULL From users Where False
But I have to name an existing table, like 'users' in this example. It works, but I would prefer a way that doesn't break if eventually the table name used is renamed or dropped.
I've tried Select NULL Where False but it doesn't work.
Using Select NULL does not return an empty set, but one row with a column named NULL and with a NULL value.
Sql Solutions
Solution 1 - Sql
There's a dummy-table in MySQL called 'dual', which you should be able to use.
select
1
from
dual
where
false
This will always give you an empty result.
Solution 2 - Sql
This should work on most DBs, tested on Postgres and Netezza:
SELECT NULL LIMIT 0;
Solution 3 - Sql
T-SQL (MSSQL):
SELECT Top 0 1;
Solution 4 - Sql
How about
SELECT * FROM (SELECT 1) AS TBL WHERE 2=3
Checked in myphp, and it also works in sqlite and probably in any other db engine.
Solution 5 - Sql
This will probably work across all databases.
SELECT * FROM (SELECT NULL AS col0) AS inner0 WHERE col0 IS NOT NULL;
Solution 6 - Sql
SELECT TOP 0 * FROM [dbo].[TableName]
This is a reasonable approach to constant scan operator.
Solution 7 - Sql
SELECT NULL WHERE FALSE;
it works in postgresql ,mysql, subquery in mysql.
Solution 8 - Sql
How about this?
SELECT 'MyName' AS EmptyColumn
FROM dual
WHERE 'Me' = 'Funny'
Solution 9 - Sql
SELECT * FROM (SELECT NULL) WHERE 0
Solution 10 - Sql
In PostgreSQL a simple
SELECT;
works. You won't even get any columns labeled 'unknown'.
Note however, it still says 1 row retrieved.