Average of Average in one row

Question

I'm not sure if this is possible what I'm trying to achieve. I want to get the avg of averaged columns.

SELECT avg(col1), avg(col2), avg(col3) FROM tbl

My Result should be the avg of all three avg columns, is this possible? Something like this

SELECT avg( col1, col2, col3) FROM tbl

doesn't work at MySQL 5.1

Answer 1

Did you try:

SELECT avg( col1 + col2 + col3)/3.0 FROM tbl

You must check that there are no nulls in this columns.

Answer 2

SELECT (AVG(col1) * COUNT(col1) +
        AVG(col2) * COUNT(col2) +
        AVG(col3) * COUNT(col3)) /
       (COUNT(col1) + COUNT(col2) + COUNT(col3))
FROM tbl