SQL: Alias Column Name for Use in CASE Statement

Question

Is it possible to alias a column name and then use that in a CASE statement? For example,

SELECT col1 as a, CASE WHEN a = \'test\' THEN \'yes\' END as value          


        

Answer 1

I think that MySql and MsSql won't allow this because they will try to find all columns in the CASE clause as columns of the tables in the WHERE clause.

I don't know what DBMS you are talking about, but I guess you could do something like this in any DBMS:

SELECT *, CASE WHEN a = 'test' THEN 'yes' END as value FROM (
   SELECT col1 as a FROM table
) q