复杂的字段加入MySQL查询

我有下面的查询，它是由一个PHP函数生成的，它变得非常复杂，但它迄今为止工作正常。复杂的字段加入MySQL查询

我想要做的就是由第二场覆盖一个场如果第三场等于1

所以我想表2 .cpda_meta_val实际上等于表3 .cpda_meta_val当表4 .cpda_meta_val等于1，这样我就可以在WHERE/ORDER BY子句中使用结果值table2.cpda_meta_val。

我希望我的理解到目前为止。

这里是原始查询：

SELECT 
    mainTable.cpda_id 
FROM 
    cp_data AS mainTable 
LEFT OUTER JOIN 
    cp_data AS table0 
     ON table0.cpda_meta_id = mainTable.cpda_id 
     AND table0.cpda_meta_key = '47248' 
LEFT OUTER JOIN 
    cp_data AS table1 
     ON table1.cpda_meta_id = mainTable.cpda_id 
     AND table1.cpda_meta_key = '47241' 
LEFT OUTER JOIN 
    cp_data AS table2 
     ON table2.cpda_meta_id = mainTable.cpda_id 
     AND table2.cpda_meta_key = '47242' 
LEFT OUTER JOIN 
    cp_data AS table3 
     ON table3.cpda_meta_id = mainTable.cpda_id 
     AND table3.cpda_meta_key = '66838' 
LEFT OUTER JOIN 
    cp_data AS table4 
     ON table4.cpda_meta_id = mainTable.cpda_id 
     AND table4.cpda_meta_key = '66843' 
LEFT OUTER JOIN 
    cp_data AS table5 
     ON table5.cpda_meta_id = mainTable.cpda_id 
     AND table5.cpda_meta_key = '47252' 
LEFT OUTER JOIN 
    cp_data AS table6 
     ON table6.cpda_meta_id = mainTable.cpda_id 
     AND table6.cpda_meta_key = '47255' 
WHERE 
    mainTable.cpda_meta_id = 47236 
    AND mainTable.cpda_active = 1 
    AND mainTable.cpda_meta_key = 'set_element_stub' 
    AND table0.cpda_meta_val = 49297 
    AND table1.cpda_meta_val != 66116 
    AND (
     table5.cpda_meta_val = 497 
     OR table6.cpda_meta_val = 497 
    ) 
ORDER BY 
    table2.cpda_meta_val, 
    mainTable.cpda_seq, 
    mainTable.cpda_id

这是我在实现上述，不工作，尝试检索没有行：

SELECT 
    mainTable.cpda_id 
FROM 
    cp_data AS mainTable 
LEFT OUTER JOIN 
    cp_data AS table0 
     ON table0.cpda_meta_id = mainTable.cpda_id 
     AND table0.cpda_meta_key = '47248' 
LEFT OUTER JOIN 
    cp_data AS table1 
     ON table1.cpda_meta_id = mainTable.cpda_id 
     AND table1.cpda_meta_key = '47241' 
LEFT OUTER JOIN 
    cp_data AS table2 
     ON table2.cpda_meta_id = mainTable.cpda_id 
     AND table2.cpda_meta_key = '47242' 
LEFT OUTER JOIN 
    cp_data AS table3 
     ON table3.cpda_meta_id = mainTable.cpda_id 
     AND table3.cpda_meta_key = '66838' 
LEFT OUTER JOIN 
    cp_data AS table4 
     ON table4.cpda_meta_id = mainTable.cpda_id 
     AND table4.cpda_meta_key = '66843' 
LEFT OUTER JOIN 
    cp_data AS table5 
     ON table5.cpda_meta_id = mainTable.cpda_id 
     AND table5.cpda_meta_key = '47252' 
LEFT OUTER JOIN 
    cp_data AS table6 
     ON table6.cpda_meta_id = mainTable.cpda_id 
     AND table6.cpda_meta_key = '47255' 
CASE 
    WHEN table4.cpda_meta_val = 1 THEN table3.cpda_meta_val 
    ELSE table2.cpda_meta_val 
END as table2.cpda_meta_val 
WHERE 
    mainTable.cpda_meta_id = 47236 
    AND mainTable.cpda_active = 1 
    AND mainTable.cpda_meta_key = 'set_element_stub' 
    AND table0.cpda_meta_val = 49297 
    AND table1.cpda_meta_val != 66116 
    AND (
     table5.cpda_meta_val = 497 
     OR table6.cpda_meta_val = 497 
    ) 
ORDER BY 
    table2.cpda_meta_val, 
    mainTable.cpda_seq, 
    mainTable.cpda_id

如果有人可以点我正确的方向，这将是伟大的！谢谢！

编辑 - 对于那些搜索，我用下面戈登的回答，使下面的查询，现在的工作：

SELECT 
    mainTable.cpda_id, 
    (CASE 
     WHEN table4.cpda_meta_val = 1 THEN table3.cpda_meta_val 
     ELSE table2.cpda_meta_val 
    END) as override_val_0 
FROM 
    cp_data AS mainTable 
LEFT OUTER JOIN 
    cp_data AS table0 
     ON table0.cpda_meta_id = mainTable.cpda_id 
     AND table0.cpda_meta_key = '47248' 
LEFT OUTER JOIN 
    cp_data AS table1 
     ON table1.cpda_meta_id = mainTable.cpda_id 
     AND table1.cpda_meta_key = '47241' 
LEFT OUTER JOIN 
    cp_data AS table2 
     ON table2.cpda_meta_id = mainTable.cpda_id 
     AND table2.cpda_meta_key = '47242' 
LEFT OUTER JOIN 
    cp_data AS table3 
     ON table3.cpda_meta_id = mainTable.cpda_id 
     AND table3.cpda_meta_key = '66838' 
LEFT OUTER JOIN 
    cp_data AS table4 
     ON table4.cpda_meta_id = mainTable.cpda_id 
     AND table4.cpda_meta_key = '66843' 
LEFT OUTER JOIN 
    cp_data AS table5 
     ON table5.cpda_meta_id = mainTable.cpda_id 
     AND table5.cpda_meta_key = '47252' 
LEFT OUTER JOIN 
    cp_data AS table6 
     ON table6.cpda_meta_id = mainTable.cpda_id 
     AND table6.cpda_meta_key = '47255' 
WHERE 
    mainTable.cpda_meta_id = 47236 
    AND mainTable.cpda_active = 1 
    AND mainTable.cpda_meta_key = 'set_element_stub' 
    AND table0.cpda_meta_val = 49297 
    AND table1.cpda_meta_val != 66116 
    AND (
     table5.cpda_meta_val = 497 
     OR table6.cpda_meta_val = 497 
    ) 
ORDER BY 
    override_val_0, 
    mainTable.cpda_seq, 
    mainTable.cpda_id

来源

2014-09-18 bbeckford

我认为第一件事 - 就是将复杂和难以理解的视为可理解的名称和含义，可以应用一些覆盖。然后重写查询，只使用必填字段并对其进行最小更改。 – 2014-09-18 15:48:21

我认为VIEWs对于这种看法来说是过分的，因为查询是通过代码生成的并且基本上是自动的。我现在使用下面的答案作为发电机弓的另一个可以说。 – bbeckford 2014-09-19 09:18:14

的case语句select子句中属于：

SELECT mainTable.cpda_id, 
     (CASE WHEN table4.cpda_meta_val = 1 THEN table3.cpda_meta_val 
      ELSE table2.cpda_meta_val 
     END) as cpda_meta_val

你可以把这个表达式直接放在order by中（这似乎是你使用的唯一地方table2_cpda_meta_val：

ORDER BY (CASE WHEN table4.cpda_meta_val = 1 THEN table3.cpda_meta_val 
       ELSE table2.cpda_meta_val 
      END), 
     mainTable.cpda_seq, 
     mainTable.cpda_id

来源

2014-09-18 15:51:03

啊当然！谢谢戈登星期五XD – bbeckford 2014-09-19 09:16:55

复杂的字段加入MySQL查询

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