Using an Alias column in the where clause in Postgresql

Question

I have a query like this:

SELECT
    jobs.*, 
    (
        CASE
            WHEN lead_informations.state IS NOT NULL THEN lead_informations.state
                   


        

Answer 1

SELECT "tab_1"."BirthDate", "tab_1"."col_1" FROM (
   SELECT BirthDate, DATEADD(year, 18, BirthDate) AS "col_1" FROM Employees
) AS "tab_1"
WHERE "tab_1"."col_1" >= '2000-12-31';