SQL count行，兩者有完全不同於表

Question

相同的外鍵我有3個表是這樣的：

CREATE TABLE Main 
(MainId INT PRIMARY KEY IDENTITY, 
Name nvarchar(50)) 

CREATE TABLE Foo 
(FooId INT PRIMARY KEY IDENTITY, 
MainId int, 
FooAnotherColumn int, 
FOREIGN KEY (MainId) REFERENCES Main(MainId) 
) 

CREATE TABLE Bar 
(BarId INT PRIMARY KEY IDENTITY, 
MainId INT, 
BarAnotherColumn INT, 
FOREIGN KEY (MainId) REFERENCES Main(MainId) 
) 

我想從名稱=一些噓聲和酒吧桌數。這是我到目前爲止的查詢。

DECLARE @fooCount int, @barCount int; 

SELECT 
    @fooCount = (SELECT 
     (COUNT(*)) 
    FROM Foo o 
    INNER JOIN Main s 
     ON o.MainId = s.MainId 
    WHERE s.Name = 'something') 

SELECT 
    @barCount = (SELECT 
     (COUNT(*)) 
    FROM Bar o 
    INNER JOIN Main s 
     ON o.MainId = s.MainId 
    WHERE s.Name = 'something') 

SELECT 
    @fooCount + @barCount; 

這是可以優化嗎？

Answer 1

就性能而言，您的查詢可能有最佳計劃。您可以將它們合併爲一個查詢：

SELECT f.foocount + b.barcount, 
FROM (SELECT COUNT(*) as foocount, 
     FROM Foo o INNER JOIN 
      Main s 
      ON o.MainId = s.MainId 
     WHERE s.Name = 'something' 
    ) f CROSS JOIN 
    (SELECT COUNT(*) as barcount 
     FROM Bar o INNER JOIN 
      Main s 
      ON o.MainId = s.MainId 
     WHERE s.Name = 'something' 
    ) b;