TSQL - how to execute a query as a variable?

Question

DECLARE @query as varchar(200);
SET @query = 'SELECT COUNT(*) FROM table';

How can I execute @query, and additionally, is there way to store the query result directly when assigning the variable?

Solution 1

You can use sp_executesql with an output parameter to retrieve the scalar result.

DECLARE @query as nvarchar(200), @count int;
SET @query = N'SELECT @count = COUNT(*)  FROM table';

EXEC sp_executesql @query, 
                   N'@count int OUTPUT', 
                   @count = @count OUTPUT

SELECT @count AS [@count]

Solution 2

You can do it like this:

exec (@query)

or, preferably, like this:

execute sp_executesql @query

For more info, check this MSDN article.

Comments

[Malyo]

Thanks, not sure if i understand the code propertly, does it asign query result into count variable, by OUTPUT?

[Martin Smith]

@Malyo - It declares a variable @count in the outer scope. This gets passed as an output parameter in the sp_executesql call which means the assignment to the output parameter is propagated to that variable. See TSQL Basics II - Parameter Passing Semantics for more about OUTPUT parameters.