获取多个表的每个租户的行数

Question

假设我有 2 个 table：Tenants 和 Wargles。 Wargles 有一个指向 Tenants 的外键，称为 TenantId。如果我想获得每个租户的 wargles 数量，我可以这样做：

SELECT t.Id as TenantId, count(w.Id) as WargleCount
FROM Tenants t
JOIN Wargles w ON w.TenantId = t.Id
GROUP BY t.Id

现在，假设我有另一个 table，Fiddles，因为 Wargles 对 Tenants 有 FK。我如何在上面的查询中添加另一列，以便获得每个租户的 wargles 数量和 fiddles 数量？

我试过这个：

SELECT t.Id as TenantId, count(w.Id) as WargleCount, count(f.Id) as FiddleCount
FROM Tenants t
JOIN Wargles w ON w.TenantId = t.Id
JOIN Fiddles f ON f.TenantId = t.Id
GROUP BY t.Id

但这行不通，因为它会为 WargleCount 和 FiddleCount 提供相同的数字，即来自 tables.

的行的乘积

Answer 1

最有效的方法可能是使用相关子查询：

SELECT t.Id as TenantId,
       (SELECT COUNT(*)
        FROM Wargles w
        WHERE w.TenantId = t.Id
      ) as WargleCount, count(f.Id) as FiddleCount
      (SELECT COUNT(*)
       FROM Fiddles f
       WHERE f.TenantId = t.Id
     ) as FiddleCount
FROM Tenants t;

特别是，这可以利用 Wargles(TenantId) 和 Fiddles(TenantId) 上的索引。

Answer 2

使用两个子选择

SELECT t.Id as TenantId, 
       (SELECT Count(1) FROM Fiddles F WHERE F.TenantId = T.Id) as FiddleCount,
       (SELECT Count(1) FROM Wargles W WHERE W.TenantId = T.Id) as WargleCount
  FROM Tenants t

Answer 3

对于您的情况，作为可扩展的解决方案，我建议使用标量函数。

/* SAMPLE DATA ARRANGE */
CREATE TABLE Tenants (Id INT, Title NVARCHAR(5)) ; INSERT INTO Tenants VALUES (1, 'A'), (2, 'B') , (3, 'C');
CREATE TABLE Wargles (Id INT,TenantId INT);INSERT INTO Wargles VALUES (1, 1), (2, 1) , (3, 1) , (4, 2), (5, 2) , (6, 1), (7, 3) , (8, 3);
CREATE TABLE Fiddles (Id INT,TenantId INT);INSERT INTO Fiddles VALUES (1, 1), (2, 1) , (3, 1) , (4, 2), (5, 2) , (6, 2), (7, 3) , (8, 2);

函数

/*NEEDED CODE*/
CREATE FUNCTION dbo.ufnGetTenantsNo ( @Id AS INT , @Tb AS INT)
RETURNS INT
AS
BEGIN
    DECLARE @Result INT = 0;

    IF (@TB = 1)
        SELECT @Result = COUNT(*)
        FROM Wargles
        WHERE TenantId = @Id
    ELSE
        SELECT @Result = COUNT(*)
        FROM Fiddles
        WHERE TenantId = @Id

    RETURN @Result
END
GO

Select声明

SELECT Id AS TenantId
    ,dbo.ufnGetTenantsNo(Id, 1) AS WargleCount
    ,dbo.ufnGetTenantsNo(Id, 2) AS FiddleCount
FROM Tenants

获取多个表的每个租户的行数

Get the number of rows per tenant of several tables

sql

sql-server

group-by

rowcount