Question

我需要在我的桌子上搜索额外的字段作为列，它使用2个不同的解决方案：

表格：方框

+ -- + ----- + ---- +
| id | name  | vinc |
|----|-------|------|
| 1  | box1  | 22   |
| 2  | box2  | 45   |
| 3  | box3  | 60   |
+ -- + ----- + ---- +

表：Extr

+ -- + ---- + ----- + ------- +
| id | vinc | type  | value   |
+----+------+-------+---------+
| 1  | 22   | color | #fafafa |
| 2  | 22   | size  | 100     |
| 3  | 45   | size  | 200     |
+ -- + ---- + ----- + ------- +

所需

+ ---- + ---- + ------- +
| name | size | color   |
+------+------+---------+
| box1 | 100  | #fafafa |
| box2 | 200  |         |
| box3 |      |         |
+ ---- + ---- + ------- +

我使用子查询并且工作了，但有时我需要通过extr.value按值搜索查询，从而产生更多进程：

SELECT 
    box.name
    ,(select extr.value from ext where extr.name = 'size' and box.vinc = extr.vinc) as size
    ,(select extr.value from ext where extr.name = 'color' and box.vinc = extr.vinc) as color
    ... 1 to X extra fields
from box
(sometimes)
where 
    (select extr.value from ext where extr.name = 'size' and box.vinc = extr.vinc) = 'user_inputed value' 
    and... 1 to X

或

SELECT 
    box.name
    ,MAX( if( extr.name = 'size' , extr.value , '' ) ) as size
    ,MAX( if( extr.name = 'color' , extr.value , '' ) ) as color
FROM box    
LEFT JOIN extr on box.vinc = extr.vinc
WHERE
   if( extr.name = 'size' , extr.value , '' ) = 'user_inputed_value'

都按框分组，所以我没有重复的行（我认为）可供选择。

这些查询具有自动构造函数，因此我不易于使用或在调试后遇到问题。

问题是：哪种最佳做法和/或性能最佳？：）

Answer 1

另一个选择是加入extr两次。

SELECT b.name, eSize.value AS size, eColor.value AS color
    , ...
FROM box AS b 
LEFT JOIN extr AS eSize ON b.vinc = eSize.vinc AND sSize.name = 'size'
LEFT JOIN extr AS eColor ON b.vinc = eColor.vinc AND eColor.name = 'color'
WHERE ...

MYSQL，MAX（IF（条件））或子查询条件下的性能

1 个答案: