mysql查询显示而不是NULL-0

我有这个疑问

SELECT
A.cod_material,
SUM(B.cantidad_pedido) as cantidad_pedido
FROM materiales AS A LEFT JOIN ingreso_material AS B 
on A.cod_material = B.cod_material GROUP BY A.cod_material;  

我的结果是

cod_material    cantidad_pedido
--------------------------------
321010001             NULL
321010002             25125
321010004             1283
321010006             NULL

我希望它显示，而不是NULL（0）

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Ty需要您的帮助

请使用

案例

SUM(case when B.cantidad_pedido IS NULL 
         then 0 
         else B.cantidad_pedido 
    end) as cantidad_pedido

或

isnull

SUM(ISNULL(B.cantidad_pedido, 0)) as cantidad_pedido

在此处使用

COALESCE（）

。函数返回第一个非空值

SELECT
  A.cod_material,
  COALESCE(SUM(B.cantidad_pedido), 0) as cantidad_pedido
FROM materiales AS A LEFT JOIN ingreso_material AS B 
  on A.cod_material = B.cod_material GROUP BY A.cod_material;  

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最好的方法是修改表并给它们一个默认值0

SELECT
  A.cod_material,
  COALESCE(SUM(B.cantidad_pedido), 0) as cantidad_pedido
FROM materiales AS A LEFT JOIN ingreso_material AS B 
  on A.cod_material = B.cod_material GROUP BY A.cod_material;