Question

My query looks like this,

SELECT field1, field2, (SELECT TOP 1 field1 from table1) as field3 
FROM table2 
HAVING field3 > 0

it throws an error

invalid column name field3

Answer 1

Don’t use a HAVING. A WHERE is more appropriate here.

SELECT field1, field2, (SELECT TOP 1 field1 from table1) as field3
FROM table2
WHERE (SELECT TOP 1 field1 from table1) > 0

Now, I am assuming that you have some work of WHERE on the sub query. That uses values from table2. Otherwise, pull that query out and assign the value to a variable.

DECLARE @field3 AS INT --change this to the correct data type
SELECT TOP 1 @field3 = field1
FROM table1

SELECT field1, field2, @field3 as field3
FROM table2
WHERE @field3 > 0

Now, only do this if you need to return empty result set. If you don’t need the empty result set, we can exclude the query all together.

DECLARE @field3 AS INT --change this to the correct data type
SELECT TOP 1 @field3 = field1
FROM table1

IF @field3 > 0
BEGIN
    SELECT field1, field2, @field3 as field3
    FROM table2
END