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

In MySql, alice name may not work, therefore put the original column name in the CASE statement

 SELECT col1 as a, CASE WHEN col1 = 'test' THEN 'yes' END as value FROM table;

Sometimes above query also may return error, I don`t know why (I faced this problem in my two different development machine). Therefore put the CASE statement into the "(...)" as below:

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