Question

I have a table like

ID Name

1 ABC
1 DEF
1 VVV
1 BBB
1 BCD
2 ZZZ
2 BAA
3 AAA
3 BBB
3 BBC

I want to get the ratio of all the names that start with A to All the names that start with B group by ID.

So the output should be

ID Ratio

1  0.5
2  0
3  0.33

.

SELECT (ID, (SELECT COUNT(*) FROM `table` WHERE name LIKE 'A%') /
            (SELECT COUNT(*) FROM `table` WHERE name LIKE 'B%')) AS `ratio` from table Group by ID 

does not give me the right answer. It takes the total ratio of A/B across all ID’s into account and writes that number for all the ID’s.

Answer 1

This will do it:

SELECT 
    id, 
    SUM(IF(name LIKE 'A%',1,0))/SUM(IF(name like 'B%',1,0)) 
FROM `table` 
GROUP BY ID