Question

我有这个问题：

UPDATE products_variants_relation SET
    state = CASE (products_id, variants_id)
        WHEN (3, 1) THEN (0)
        WHEN (3, 2) THEN (4)
        WHEN (3, 3) THEN (3)
        WHEN (3, 4) THEN (0)
    END
WHERE (products_id, variants_id) IN ((3, 1),(3, 2),(3, 3),(3, 4))

正如您可能看到的，由于性能原因，我尝试进行多次更新。我的想法是通过组合(products_id, variants_id)找到行，并使用正确的值更新另一个字段state。我试图删除THEN后面的值的括号，但后来我遇到了语法错误。

如果没有元组（对），这个多次更新技巧很有用。在这种特殊情况下，MySQL会抛出错误：

#1241 - Operand should contain 1 column(s)

如何更改查询以便我可以使用对进行多次更新？提前谢谢。

修改感谢@ gordon-linoff我解决了它。实际上，这也是正确的：

UPDATE products_variants_relation
    SET state = (CASE
        WHEN products_id = 3 and variants_id = 1 THEN 0
        WHEN products_id = 3 and variants_id = 2 THEN 4
        WHEN products_id = 3 and variants_id = 3 THEN 3
        WHEN products_id = 3 and variants_id = 4 THEN 0
    END)
WHERE (products_id, variants_id) IN ((3, 1),(3, 2),(3, 3),(3, 4))

因此，允许where子句中的元组。

Answer 1

使用and和or：

UPDATE products_variants_relation
    SET state = (CASE WHEN products_id = 3 and variants_id = 1) THEN 0
                      WHEN products_id = 3 and variants_id = 2) THEN 4
                      WHEN products_id = 3 and variants_id = 3) THEN 3
                      WHEN products_id = 3 and variants_id = 4) THEN 0
                 END)
   WHERE (products_id = 3 and variants_id = 1) OR
         (products_id = 3 and variants_id = 2) OR
         (products_id = 3 and variants_id = 3) OR
         (products_id = 3 and variants_id = 4);

in和case都不接受MySQL中的元组（请参阅here）。

您可能会发现使用join更容易做到：

UPDATE products_variants_relation pvf
       (select 3 as pid, 1 as vid, 0 as val union all
        select 3, 2, 4 union all
        select 3, 3, 3 union all
        select 3, 4, 0
       ) newvals
       ON pvf.products_id = newvals.pid and pvf.variants_id = newvals.vid
    SET pvf.state = newvals.val;

join执行过滤并匹配值。

带有元组的MySQL CASE语句

1 个答案: