How to conditionally handle division by zero with MySQL

Question

In MySQL, this query might throw a division by zero error:

SELECT ROUND(noOfBoys / noOfGirls) AS ration
FROM student;

If noOfGirls

Answer 1

You can use this (over-expressive) way:

select IF(noOfGirls=0, NULL, round(noOfBoys/noOfGirls)) as ration from student;

Which will put out NULL if there are no girls, which is effectively what 0/0 should be in SQL semantics.

MySQL will anyway give NULL if you try to do 0/0, as the SQL meaning fo NULL is "no data", or in this case "I don't know what this value can be".