Question

There are two tables: A, with rows (row_id, column1, …) and B, with rows (column2, …).

Select * from A
   join B on A.column1 = B.column2

There can be 1 or more records in table B having column2 = A.column1. Every record in B has a matching record in A, but not every record in A has records in B.

What is an efficient query to get the row_id in table A, that has more than 100 records in table B associated with it?

Answer 1

SELECT `row_id`
FROM `A`
JOIN `B` ON (`B`.`column2` = `A`.`column1`)
GROUP BY `A`.`row_id`
HAVING COUNT(*) > 100