Why can't I use column aliases in the next SELECT expression?

Question

Can I modify the next to use the column aliases avg_time and cnt in an expression ROUND(avg_time * cnt, 2)?

SELECT 
           


        

Answer 1

Either repeat the expressions:

ROUND(ROUND(AVG(time), 2) * COUNT(path), 2) as slowdown

or use an subquery:

SELECT *, ROUND(avg_time * cnt, 2) as slowdown FROM (
  SELECT 
    COALESCE(ROUND(stddev_samp(time), 2), 0) as stddev_time, 
    MAX(time) as max_time, 
    ROUND(AVG(time), 2) as avg_time, 
    MIN(time) as min_time, 
    COUNT(path) as cnt, 
    path
  FROM loadtime
  GROUP BY path) x
ORDER BY avg_time DESC
LIMIT 10;