来自两个不同表的SQL计数行，其中两个表都具有来自完全不同表的相同外键

我有3张这样的桌子：

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)
)

我想从boo和bar表中计算Name=something。这是我到目前为止提出的问题

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;

---

这是可以优化的吗？

就性能而言，您的查询可能有最好的计划。您可以将它们组合到单个查询中：

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;