MySQL組合表錯誤查詢

我在單獨的查詢中查詢兩個表。這樣做會在不到一秒的時間內產生正確的結果，但是，如果我嘗試合併它們，則需要很長時間才能殺死查詢（大量記錄）。我想知道我做錯了什麼。MySQL組合表錯誤查詢

所需的輸出

+--------+-----------+-----------+-----------+  
| name | computers | printers | tvs  | 
+--------+-----------+-----------+-----------+ 
| Peter | 12  | 1  | 5  | 
| Josh | 20  | 4  |   | 
| Bob | 15  | 4  | 9  | 
+--------+-----------+-----------+-----------+

查詢1

SELECT 
    names.name, 
    SUM(IF(pcs.electronic = 'computers', 1,0)) AS computers, 
    SUM(IF(pcs.electronic = 'printers', 1,0)) AS printers 
FROM 
    electronics.pcs LEFT JOIN electronics.orders 
    ON pcs.id = orders.id 
    LEFT JOIN electronics.buying 
    ON orders.id = buying.id 
    LEFT JOIN dbnames.names names 
    ON names.clientid = pcs.clientid 
WHERE 
    pcs.clientid IS NOT NULL AND 
    pcs.belongs IN (10) 
GROUP BY pcs.clientid

表1 - 查詢1

+--------+-----------+-----------+ 
| name | computers | printers | 
+--------+-----------+-----------+ 
| Peter | 12  | 1  | 
| Josh | 20  | 4  | 
| Bob | 15  | 4  | 
+--------+-----------+-----------+

查詢2

SELECT 
    names.name, 
    SUM(IF(tvs.electronic = 'tvs', 1,0)) AS tvs 
FROM 
    electronics.tvs LEFT JOIN dbnames.names names 
    ON names.clientid = tvs.clientid 
WHERE 
    tvs.belongs IN (10) 
GROUP BY tvs.clientid

表2 - 查詢2

+--------+-----------+ 
| name | tvs  | 
+--------+-----------+ 
| Peter | 5  | 
| Bob | 9  | 
+--------+-----------+

來源

2011-02-15 Mike79

大，謝謝大家！ – Mike79 2011-02-15 05:18:27

爲什麼不能做一個簡單的UNION？

SELECT 
    names.name, 
    SUM(IF(pcs.electronic = 'computers', 1,0)) AS computers, 
    SUM(IF(pcs.electronic = 'printers', 1,0)) AS printers 
FROM 
    electronics.pcs LEFT JOIN electronics.orders 
    ON pcs.id = orders.id 
    LEFT JOIN electronics.buying 
    ON orders.id = buying.id 
    LEFT JOIN dbnames.names names 
    ON names.clientid = pcs.clientid 
WHERE 
    pcs.clientid IS NOT NULL AND 
    pcs.belongs IN (10) 
GROUP BY pcs.clientid 

UNION ALL 

SELECT 
    names.name, 
    SUM(IF(tvs.electronic = 'tvs', 1,0)) AS tvs 
FROM 
    electronics.tvs LEFT JOIN dbnames.names names 
    ON names.clientid = tvs.clientid 
WHERE 
    tvs.belongs IN (10) 
GROUP BY tvs.clientid

只是一個想法...

來源

2011-02-15 03:03:25 Eli

我想知道，你不需要一個平等的專欄所有列？也將結合記錄的結果集，但我需要的是額外的列。 – Mike79 2011-02-15 03:09:03

你對我的道歉是正確的，我正在考慮@cyberkiwi，只是出錯了:)。你可能需要一種`FULL JOIN`或'FULL OUTER JOIN`，就像他提到的那樣，而不是`UNION`。無論如何感謝 – Eli 2011-02-15 03:30:07

一個完整的加盟將很好地工作，但是因爲MySQL不支持全加入..你可以UNION ALL兩者之間，並從對應的列坐MAX 。

SELECT clientid, name, 
    MAX(computers) computers, 
    MAX(printers) printers, 
    MAX(tvs) tvs 
FROM 
(
    SELECT 
     pcs.clientid, 
     names.name, 
     SUM(IF(pcs.electronic = 'computers', 1,0)) AS computers, 
     SUM(IF(pcs.electronic = 'printers', 1,0)) AS printers, 
     NULL 
    FROM 
     electronics.pcs LEFT JOIN electronics.orders 
     ON pcs.id = orders.id 
     LEFT JOIN electronics.buying 
     ON orders.id = buying.id 
     LEFT JOIN dbnames.names names 
     ON names.clientid = pcs.clientid 
    WHERE 
     pcs.clientid IS NOT NULL AND 
     pcs.belongs IN (10) 
    GROUP BY pcs.clientid, names.name 
    UNION ALL 
    SELECT 
     tvs.clientid, 
     names.name, 
     NULL, NULL, 
     SUM(IF(tvs.electronic = 'tvs', 1,0)) AS tvs 
    FROM 
     electronics.tvs LEFT JOIN dbnames.names names 
     ON names.clientid = tvs.clientid 
    WHERE 
     tvs.belongs IN (10) 
    GROUP BY tvs.clientid, names.name 
) Q2 
GROUP BY clientid, name

來源

2011-02-15 03:03:30 RichardTheKiwi

select * 
from 
(
    ... first query 
) as query1 
left join 
(
    ... second query 
) as query2 
on query1.name=query2.name;

來源

2011-02-15 05:11:53 ajreal

MySQL組合表錯誤查詢

回答

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