PostgreSQL check value from sum in where

Question

I'm triyng to add a the done value to where clause, so I can show only results from todo, that are already done, but keep getting an error:

select "todo", SUM( "test"."count" ) as "done"
from B 
Where "done" =  "todo"

this is the error:

q_driver: [PGRES_FATAL_ERROR]ERRORE: the column "done" don't exist

but the column is displayed if I remove the where clause

Answer 1

You cannot use alias name in same select query where clause

select * from
(
select "todo", SUM( "test"."count" ) as "done"
from B 
GROUP BY "todo"
)
Where "done" =  "todo"