SQL - 按不同值分組

我的問題是否有更快的方式來查詢以下內容？SQL - 按不同值分組

我使用Oracle 10g

說我有一個表，製造商和汽車，我要算列「Car.Name」的所有事件。這裏是我會怎麼做它：

SELECT manuf.Name, COUNT(car1.Name), COUNT(car2.Name), COUNT(car3.Name) 
FROM Manufacturer manuf 
LEFT JOIN (SELECT * FROM Car c where c.Name = 'Ferrari1') car1 ON manuf.PK = car1.ManufPK 
LEFT JOIN (SELECT * FROM Car c where c.Name = 'Ferrari2') car2 ON manuf.PK = car2.ManufPK 
LEFT JOIN (SELECT * FROM Car c where c.Name = 'Ferrari3') car3 ON manuf.PK = car3.ManufPK 
GROUP BY manuf.Name

通緝結果：

Manufacturer | Ferrari1 | Ferrari2 | Ferrari3 
---------------------------------------------- 
Fiat   | 1  | 0  | 5 
Ford   | 2  | 3  | 0

我很少LEFT JOIN的嘗試這樣做，它工作得很好。但是當我添加了很多（如90+）時，它超慢（超過1分鐘）。

我的問題，有沒有更快的方法來做這個查詢？

來源

2012-01-25 WoF_Angel

你能告訴我們什麼是你以前的查詢？ – everton

@WoF_Angel您使用哪種RDBMS？在MySQL中，您可以考慮在MSSQL中使用'GROUP_CONCAT'關於'PIVOT' –

[通過正確的索引，多個連接可能至少會像PIVOT/GROUP BY一樣執行]（http://stackoverflow.com/questions/ 7448453/sql-server-pivot-vs-multiple-join/7449213＃7449213） –

如果你很高興看到汽車倒計時頁面，請嘗試：

select m.Name manufacturer_name, 
     c.Name car_name, 
     count(*) 
from Manufacturer m 
left join Car c 
     on m.PK = c.ManufPK and c.Name in ('Ferrari1','Ferrari2','Ferrari3') 
group by m.Name, c.Name

如果你需要看到整個頁面各個汽車，嘗試：

select m.Name manufacturer_name, 
     sum(case c.Name when 'Ferrari1' then 1 else 0 end) Ferrari1_Count, 
     sum(case c.Name when 'Ferrari2' then 1 else 0 end) Ferrari2_Count, 
     sum(case c.Name when 'Ferrari3' then 1 else 0 end) Ferrari3_Count 
from Manufacturer m 
left join Car c 
     on m.PK = c.ManufPK and c.Name in ('Ferrari1','Ferrari2','Ferrari3') 
group by m.Name

來源

2012-01-25 11:43:53

他提到過。 – everton

@aF那麼是什麼？這不適合需求 - 所以我們需要一些細化的問題 –

我用你的第二個建議，工作得很好。謝謝。 –

SELECT manuf.Name, COUNT(DISTINCT c.Name) 
FROM Manufacturer manuf 
LEFT JOIN Car c ON manuf.PK = c.ManufPK 
GROUP BY manuf.Name

OR根據您的需要

SELECT manuf.Name, c.Name, COUNT(*) Cnt 
FROM Manufacturer manuf 
LEFT JOIN Car c ON manuf.PK = c.ManufPK 
GROUP BY manuf.Name, c.Name

PS：你的問題不是很清楚。提供了一些有用的結果集細化答案

來源

2012-01-25 11:42:20

這不會給出同一行中的所有計數。 –

@MarkBannister查看評論回覆 –

你也可以試試這個：

SELECT manuf.Name 
    , car1.cnt AS Ferrari1 
    , car2.cnt AS Ferrari2 
    , car3.cnt AS Ferrari3 
FROM 
     Manufacturer AS manuf 
    LEFT JOIN 
     (SELECT ManufPK, COUNT(*) AS cnt 
     FROM Car 
     WHERE Name = 'Ferrari1' 
     GROUP BY ManufPK 
    ) AS car1 
    ON car1.ManufPK = manuf.PK 
    LEFT JOIN 
     (SELECT ManufPK, COUNT(*) AS cnt 
     FROM Car 
     WHERE Name = 'Ferrari2' 
     GROUP BY ManufPK 
    ) AS car2 
    ON car2.ManufPK = manuf.PK 
    LEFT JOIN 
     (SELECT ManufPK, COUNT(*) AS cnt 
     FROM Car 
     WHERE Name = 'Ferrari3' 
     GROUP BY ManufPK 
    ) AS car3 
    ON car3.ManufPK = manuf.PK 
ORDER BY manuf.Name

來源

2012-01-25 13:07:49

SQL - 按不同值分組

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