Question

我正在尝试使用不同的表进行嵌套选择。这是我的疑问：

SELECT contact_profile.name, main_app.fk_lkp_app, main_app.id as main_id,
(
    -- if the main_app.fk_lkp_app value is 1 then do this
    SELECT SUM(translation_app.amount)
    FROM translation_app
    WHERE translation_app.fk_main_app = main_app.id 
    AND translation_app.status = 2 
    AND main_app.srf_number is not null 
    AND main_app.fk_invoice is not null

    -- if the main_app.fk_lkp_app value is 2 then do this
    SELECT SUM(interpretation_app.amount)
    FROM interpretation_app
    WHERE interpretation_app.fk_main_app = main_app.id 
    AND interpretation_app.status =2 
    AND main_app.srf_number is not null 
    AND main_app.fk_invoice is not null

    -- if the main_app.fk_lkp_app value is 3 then do this
    SELECT SUM(course_app.amount)
    FROM course_app
    WHERE course_app.fk_main_app = main_app.id
    AND course_app.status =2
    AND main_app.srf_number is not null 
    AND main_app.fk_invoice is not null
) as amount
FROM contact_profile
LEFT JOIN main_app ON main_app.fk_contact_profile = contact_profile.id 
WHERE main_app.fk_lkp_app in (1,2,3) 
AND main_app.srf_number is not null 
AND main_app.fk_invoice is not null 
GROUP BY contact_profile.name
ORDER BY amount DESC

如您所见，“amount”字段是根据main_app.fk_lkp_app值从不同的表中选择的。问题是如何进行此查询的最佳方法？我坚持使用“main_app.fk_lkp_app”值参数部分。

我甚至尝试过按照建议使用CASE，但它一直给我错误代码＃1064

SELECT contact_profile.name, main_app.fk_lkp_app, main_app.id as main_id,
(
CASE 
    WHEN main_app.fk_lkp_app = '1' 
    THEN (  
        SELECT SUM(translation_app.amount)
        FROM translation_app
        WHERE translation_app.fk_main_app = main_app.id 
    )
    WHEN main_app.fk_lkp_app = '2' 
    THEN (
        SELECT SUM(interpretation_app.amount)
        FROM interpretation_app
        WHERE interpretation_app.fk_main_app = main_app.id 
    )
    WHEN main_app.fk_lkp_app = '3' 
    THEN (
        SELECT SUM(course_app.amount)
        FROM course_app
        WHERE course_app.fk_main_app = main_app.id
    )
    ELSE 0
END CASE
) as amount
FROM contact_profile
LEFT JOIN main_app ON main_app.fk_contact_profile = contact_profile.id 
WHERE main_app.fk_lkp_app in (1,2,3) 
AND main_app.srf_number is not null 
AND main_app.fk_invoice is not null 
GROUP BY contact_profile.name
ORDER BY amount DESC

奇怪的是，如果我不使用大小写并且只使用3变量中的1个选择（例如我只从translation_app表中选择），则查询正在运行。

Answer 1

您可以使用CASE表达式检查main_app.fk_lkp的值

http://dev.mysql.com/doc/refman/5.7/en/control-flow-functions.html#operator_case

并根据该值执行查询。我无法测试它，但这样的事情应该起作用

SELECT contact_profile.name, main_app.fk_lkp_app, main_app.id as main_id,
CASE
    WHEN  main_app.fk_lkp_app = 1 THEN (/* your query here */)
    WHEN  main_app.fk_lkp_app = 2 THEN (/* your query here */)
    WHEN  main_app.fk_lkp_app = 2 THEN (/* your query here */)
    ELSE 0
END AS amount ....

嵌套选择来自不同的表

1 个答案: