Select 来自相同 table 的另一个列值，如果另一个列值为 NULL
Select another column value from the same table if another column value is NULL
我有一个包含四列的 table：NAME、AGE、PRIMARYWEIGHT 和 SECONDARYWEIGHT
Where NAME = 'Damian'，我希望 select AGE 和 PRIMARYWEIGHT 只有当 SECONDARYWEIGHT 是 NULL 否则我会 PRIMARYWEIGHT.
理想情况下，我想给它起一个别名 'WEIGHT'，不管它是 PRIMARYWEIGHT 还是 SECONDARYWEIGHT。
SELECT NAME, AGE, ISNULL(PRIMARYWEIGHT, SECONDARYWEIGH) As WEIGHT
SELECT AGE, COALESCE(SECONDARYWEIGH, PRIMARYWEIGHT) As WEIGHT
您可以使用 COALESCE（如您的标签所示）
Evaluates the arguments in order and returns the current value of the first expression that initially does not evaluate to NULL.
我有一个包含四列的 table：NAME、AGE、PRIMARYWEIGHT 和 SECONDARYWEIGHT
Where NAME = 'Damian'，我希望 select AGE 和 PRIMARYWEIGHT 只有当 SECONDARYWEIGHT 是 NULL 否则我会 PRIMARYWEIGHT.
理想情况下，我想给它起一个别名 'WEIGHT'，不管它是 PRIMARYWEIGHT 还是 SECONDARYWEIGHT。
SELECT NAME, AGE, ISNULL(PRIMARYWEIGHT, SECONDARYWEIGH) As WEIGHT
SELECT AGE, COALESCE(SECONDARYWEIGH, PRIMARYWEIGHT) As WEIGHT
您可以使用 COALESCE（如您的标签所示）
Evaluates the arguments in order and returns the current value of the first expression that initially does not evaluate to NULL.