当查询结果为空时，如何强制MySQL查询返回0？

Question

I have the following query:

SELECT 
SUM(quantity) AS qt
FROM 
stockMove
WHERE
date_mov >= '2019-04-01'
AND
date_mov <= '2019-04-30'
AND
ProductCode = '000807'
GROUP BY 
ProductCode 

If a have no movement of this product in this date range, the query returns nothing, but I need that to return 0.

I already try:

SELECT SUM(quantity) AS qt, COALESCE(quantity, 0)

and

SELECT SUM(quantity) AS qt, IFNULL(quantity, 0)

but the query still returns 0 rows.

Is there a way to resolve my issue?

Thanks guys.

Answer 1

如下使用

SELECT COALESCE(SUM(quantity),0) AS qt

Answer 2

In your case, just remove the GROUP BY and use COALESCE() :

SELECT COALESCE(SUM(quantity), 0) AS qt
FROM stockMove
WHERE date_mov >= '2019-04-01' AND date_mov <= '2019-04-30' AND
      ProductCode = '000807';

An aggregation query with no GROUP BY always returns one row, even when no rows match. The returned value is NULL -- which is where the COALESCE() comes in.

With the GROUP BY , the query returns no rows at all. Can't convert nothing into a 0 .