Question

我有以下SQL语句，我正在尝试更新与select语句匹配的多行。

UPDATE Cars
SET engineSize = CASE specCode WHEN 1 THEN value ELSE engineSize END
FROM Cars
INNER JOIN CarSpecs ON CarsSpecs.carID = Cars.carID

我的表格如下：

Cars

carID   engineSize ...
1       0
2       0

CarSpecs

carID   specCode    value
1       1           1800
1       2           Blue
1       3           Petrol
2       1           2200
2       2           Green
2       3           Petrol

specCode涉及我想在Cars表中更新的一种规范（1是引擎大小）

当我运行查询时，它每次都会返回NULL。我看到它的方式应该找到specCode = 1并将engineSize设置为1800然后在设置之后将其设置为第一个找到的值。

有什么想法吗？

修改：我需要更新Cars表中的多个列。这就是使用CASE的原因，即：

UPDATE Cars 
SET engineSize = CASE specCode WHEN 1 THEN value ELSE engineSize END,
colour = CASE specCode WHEN 2 THEN value ELSE colour END
FROM Cars
INNER JOIN CarSpecs ON CarsSpecs.carID = Cars.carID

Answer 1

要更新多个列，在您的情况下，您需要多个连接（如Martin所示）

UPDATE Cars
SET  engineSize = CarSpecs1.value, colour = CarSpecs2.value
FROM Cars
INNER JOIN CarSpecs CarSpecs1 
    ON CarsSpecs1.carID = Cars.carID AND CarsSpecs1.specCode =1
INNER JOIN CarSpecs CarSpecs2 
    ON CarsSpecs2.carID = Cars.carID AND CarsSpecs2.specCode =2

使用OUTER连接并非为每辆车存储所有规格。

Answer 2

如果马丁的解决方案不起作用（当它运行三次时）你也可以立刻做到这一点......虽然有点尴尬：

UPDATE Cars
SET Cars.engineSize = (SELECT value FROM CarSpecs WHERE CarSpecs.carId = Cars.carID AND CarSpecs.specCode = 1),
SET Cars.colour = (SELECT value FROM CarSpecs WHERE CarSpecs.carId = Cars.carID AND CarSpecs.specCode = 2),
SET Cars.fuel = (SELECT value FROM CarSpecs WHERE CarSpecs.carId = Cars.carID AND CarSpecs.specCode = 3)
FROM Cars

Answer 3

UPDATE empsal SET sal =
  CASE WHEN sal BETWEEN 100 AND 500 THEN sal + 400
    WHEN sal BETWEEN 1000 AND 2000 THEN sal + 1000
    else sal
  END

ELSE部分不是强制性的。但如果不存在，则所有未评估的案例都将替换为NULL。

在SQL 2008中使用CASE更新多行

3 个答案: