Question

I’m trying to insert a record if a sum of 3 user columns from 2 tables exceeds a constant.

I’ve searched all over, found you can’t put user variables in IFs, WHERE‘s etc. Found you can’t put SUMs in IFs, WHERE‘s etc. I’m at a total loss. Here’s an example of my earlier bad code before unsuccessfully trying to use SUMs in WHEREs, if it helps:

SELECT SUM(num1) INTO @mun1 FROM table1 WHERE user = '0';

SELECT SUM(num2) INTO @mun2 FROM table1 WHERE user = '0';

SELECT SUM(num3) INTO @mun3 FROM table2 WHERE column1 = 'd' AND user = '0';

SET @mun4 = @mun1 - @mun2 - @mun3;

INSERT INTO table2 (user, column1, column2) VALUES ('0', 'd', '100') WHERE @mun4 >= 100;

Answer 1

Try this:

INSERT INTO table2 (user, column1, column2) 
select '0', 'd', '100'
from dual
where (SELECT SUM(num1 + num2) FROM table1 WHERE user = '0') +
      (SELECT SUM(num3) FROM table2 WHERE column1 = 'd' AND user = '0') > 100;

This is a case of the general solution for a “insert if condition” problem:

insert into ... select ... where condition

The select will only return rows if the condition is true, and importantly, will return no rows if false – meaning the insert only happens if the condition is true, otherwise nothing happens.