I want to delete all rows which has no existing foreign key in another table example:
table1
+----+-------+
|id | data |
+----+-------+
| 1 | hi |
+----+-------+
| 2 | hi |
+----+-------+
| 3 | hi |
+----+-------+
| 4 | hi |
+----+-------+
| 5 | hi |
+----+-------+
table2
+----+-------+
|a_id| data |
+----+-------+
| 1 | hi |
+----+-------+
| 20 | hi |
+----+-------+
| 3 | hi |
+----+-------+
| 40 | hi |
+----+-------+
| 5 | hi |
+----+-------+
The query will delete rows with id# 20 and 40 on table2.
I need to do this so that i could establish a relationship with table1 and table2.