Admin
1
I need to use an alias in the WHERE clause, but It keeps telling me that its an unknown column. Is there any way to get around this issue? I need to select records that have a rating higher than x. Rating is calculated as the following alias:
sum(reviews.rev_rating)/count(reviews.rev_id) as avg_rating
You could use a HAVING clause, which can see the aliases, e.g.
HAVING avg_rating>5
but in a where clause you'll need to repeat your expression, e.g.
WHERE (sum(reviews.rev_rating)/count(reviews.rev_id))>5
BUT! Not all expressions will be allowed - using an aggregating function like SUM will not work, in which case you'll need to use a HAVING clause.
From the MySQL Manual:
It is not allowable to refer to a column alias in a WHERE clause, because the column value might not yet be determined when the WHERE clause is executed. See Section B.1.5.4, “Problems with Column Aliases”.
I don't know if this works in mysql, but using sqlserver you can also just wrap it like:
select * from (
-- your original query
select .. sum(reviews.rev_rating)/count(reviews.rev_id) as avg_rating
from ...) Foo
where Foo.avg_rating ...
SELECT * FROM (SELECT customer_Id AS 'custId', gender, age FROM customer
WHERE gender = 'F') AS c
WHERE c.custId = 100;