Question

Due to the syntax of mySQL this statement is not allowed (a counted element cannot be used within the WHERE part):

Illegal syntax:
SELECT COUNT(x) AS amount ... WHERE amount > 0

But how do I handle a COUNTed element via WHERE ?

Answer 1

edit

Note that your original query may not do what you think it does. You probably want WHERE x > 0 instead:

SELECT COUNT(x) AS amount ... WHERE x > 0

This is because HAVING amount > 0 is essentially meaningless if there are ANY x values greater than 0. MySQL will automatically group and include all of your rows, counting every one of them. It looks like you want to know the number of rows with a non-zero amount in x, so you need to specify with WHERE that only those rows should match the original criteria to be counted. See below for an example case of needing an aggregate function with HAVING.

original answer:

You do this with HAVING. The syntax is exactly the same as WHERE, but it is evaluated after the aggregation.

SELECT COUNT(x) AS amount ... HAVING amount > 0

The difference is important, since it allows you to limit which rows are counted with WHERE, and then limit the rows returned with HAVING.

For instance, let’s say I wanted to know how much money I made per department on sales of LESS THAN $10, only if it made more than $1000:

SELECT 
  SUM(amount) as total_sales
  ... 
WHERE amount < 10.0 
GROUP BY department 
HAVING total_sales > 1000.0