Question

I have a problem. I have 3 tables like below:

1) met_ID (primair) etc.

2) magn_ID (primair)
met_ID (secondary)
…

3) sens_ID (primair)
met_ID (secondary)
…

I have to delete records in table 1 where met_ID count in table 2 OR 3 is less than 10..

SELECT COUNT(*) AS count, met_ID
FROM tbl_1, tbl_2
Where met_ID = met_ID
GROUP BY met_ID

I made a query and in PHP with WHILE loop i am deleting that records from table 1. It works fine for 1000 records to delete, but I am not sure if it will be use full for 100 000 or more records in table.

Is there any way to accomplish what i do in sql query?

Answer 1

DELETE from tbl_1
WHERE 10 > (select count(*) from tbl_2 where tbl2.met_id=tbl1.met_id) OR
      10 > (select count(*) from tbl_3 where tbl3.met_id=tbl1.met_id)