Execute dynamic query stored as varchar in a different table.

Question

Hi,
I have a table with a column as query,which stores the query i want to fire.for eg.my query will be like :-
Select name,empid from employees where name =null
Now,I have a stored procedure in which i have declared  a variable @query .I want to replace the following line of code .
if exists(Select name ,empid from employees where name=null)
begin
--send mail
end
as
if exists(@query)
But it doesnt seem to work because it is taking the @query as varchar and not an actual t-sql command.I want to keep the query dynamic as each row in my table has a different query to fire.

Answer 1

And only to clarify Praveen's solution:
DECLARE @DynamicSQl nvarchar(250), @x nvarchar(100)
SELECT @x = '@retVal int output'
DECLARE @retVal int
SET @DynamicSQl = 'SET @retVal = CASE WHEN EXISTS (' + @query + ') THEN 1 ELSE 0 END'
EXEC sp_executesql @DynamicSQl, @x, @retVal output
IF @retVal > 0
BEGIN
print 'send mail'
END
However, Nimo should probably have some error handling, as the stored query may not be syntactically correct. And even if it is syntactically correct, it may not play well with EXISTS. Case in point: a query that starts with a CTE.
And of course, if any user is permitted to add these queries, and this code is exeuted with high permissions, they can inject queries that perform evil things they don't have permissions to do themselves, so be careful.
Erland Sommarskog, SQL Server MVP, [email protected]