从两个表中减去列

Question

I have two tables from which I need to subtract two columns

My query for that:

SELECT
  `T1`.`Code`,
  (Sum(`T1`.`Qty`) - Sum(`T2`.`Qty`)) AS TotalQty
FROM
  `T1`
  LEFT JOIN `T2` ON `T1`.`Code` =
    `T2`.`Code`
GROUP BY
  `T1`.`Code`

This works fine if I have data in table T2, but if there is no data than I get null as result for TotalQty even if T1 are some records. How to get correct calculation even there is no data in T2?

Answer 1

Try this..

SELECT
  `T1`.`Code`,
  (IFNULL(Sum(`T1`.`Qty`),0) - IFNULL(Sum(`T2`.`Qty`),0)) AS TotalQty
FROM
  `T1`
  LEFT JOIN `T2` ON `T1`.`Code` =
    `T2`.`Code`
GROUP BY
  `T1`.`Code`