Question

How can I combine the columns returned by two SELECT statements to give their element-wise quotient?

Query 1:

SELECT COUNT(*) AS count
FROM table1
WHERE col2 = 1 AND col3 > 5
GROUP BY col4
ORDER BY col4

Query 2:

SELECT COUNT(*) AS count
FROM table1
WHERE col2 = 1
GROUP BY col4
ORDER BY col4

So if they return something like:

Query 1        Query 2
count           count
-----------------------
1              5
2              4

I will get:

quotient
-------
0.2
0.5

Answer 1

With the 4-column version of the question, we can assume that the quotient is between groups with the same value in col4. So, the answer becomes:

SELECT col4, SUM(CASE WHEN col3 > 5 THEN 1 ELSE 0 END) / COUNT(*) AS quotient
  FROM table1
 WHERE col2 = 1
 GROUP BY col4;

I’ve retained col4 in the output because I don’t think the ratios (quotients) will be useful without something to identify which quotient is associated with which values, though theoretically, the answer doesn’t want that column in the output.