SELECT 来自 Where 子句中的多个 IF 条件

Question

我有以下查询

SELECT *
FROM products a, productImgs b
WHERE a.visible = 1 AND a.Type IN ('Accessories', 'Clothing', 'Electronics')
ORDER BY a.visibleOrder ASC
LIMIT 100

在上面的查询中，我需要添加 IF 条件，即 IF a.Type 是 Accessories then I need certain a.Brands to select from and if a.Type is Clothing then我需要 select 来自某些 a.Brands

For a.Type 'Accessories' ->  a.Brands IN (ALL)
For a.Type 'Clothing'    ->  a.Brands IN ('A','B','C')
For a.Type 'Electronics' ->  a.Brands IN ('D','E','F')

Answer 1

使用 CASE 表达式，但您还应该为 2 个表编写一个带有 ON 子句的正确连接：

SELECT * 
FROM products a INNER JOIN productImgs b
ON .....
WHERE a.visible=1 
  AND CASE a.Type 
        WHEN 'Accessories' THEN 1
        WHEN 'Clothing' THEN a.Brands IN ('A','B','C')
        WHEN 'Electronics' THEN a.Brands IN ('D','E','F')
      END 
ORDER BY a.visibleOrder ASC LIMIT 100;

Answer 2

像使用任何其他 where 子句一样使用括号和 and/or 条件：

where a.visible = 1 and (
  a.Type = 'Accessories' or
  a.Type = 'Clothing'    and a.Brands IN ('A', 'B', 'C') or
  a.Type = 'Electronics' and a.Brands IN ('D', 'E', 'F')
)

这应该 MySQL 有机会使用索引。

SELECT 来自 Where 子句中的多个 IF 条件

SELECT from Multiple IF conditions in Where Clause

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