Sql 从多个表中选择

表B、表c

表A的ID为col1

ID    COL1
1      abc
2      bcd

表B中有col2、col3

col2 col3
bcc  abc
acc  bcd

表C具有ID col4

ID col3
1   qwe
1   tre
1   uid
2   jkj
2   jwekj

现在，我需要选择ID，COL1，COL2，count（表C中的ID）。示例输出将是

ID  COL1  COL2  CNT
1   abc   bcc    3
2   bcd   acc    2

---

谁能帮我一下吗？表A和表B使用COl1和COL3连接。

为什么不按ID连接表A和表C并获取计数

select  a.id
,       max(a.col1)
,       avg(b.col2)
,       count(distinct c.ID)
from    TableA a
join    TableA b
on      a.col1 = b.col3
left join
        TableC c
on      c.id = a.id
group by
        a.id

SELECT TableA.ID, TableA.COL1, TableB.COL2, COUNT(TableC.*)
FROM TableA
INNER JOIN TableB ON TableB.COL3 = TableA.COL1
INNER JOIN TableC ON TableC.ID = TableA.ID
GROUP BY TableA.ID, TableA.COL1, TableB.COL2
ORDER BY TableA.ID, TableA.COL1, TableB.Col2

---

也许是这样的：

SELECT
    TableA.COL1,
    TableB.col2,
    (
        SELECT
            COUNT(*)
        FROM
            TableC
        WHERE
            TableC.ID=TableA.ID
    )
FROM
    TableA
    JOIN TableB
        ON TableA.COL1=TableB.col3

---

您使用的是哪个版本的sql server？我们只能通过在id列上分组来获取吗？请看@Arion的回答表a中的所有id不需要出现在表C中。因此，我需要从表中获取所有值。如果该ID不在表C中，则该计数应为0。只有我在这里找不到它。我试着用左外接。但仅按ID分组会让我很不舒服。编辑后，它只按ID分组，但这意味着您必须将其他列放入聚合函数中，如min、max或avg

SELECT
    TableA.COL1,
    TableB.col2,
    (
        SELECT
            COUNT(*)
        FROM
            TableC
        WHERE
            TableC.ID=TableA.ID
    )
FROM
    TableA
    JOIN TableB
        ON TableA.COL1=TableB.col3

Select 
    a.Id, a.col1, b.col2, count(c.*) As Cnt
From A as a
Inner Join B as b on a.col1 = b.col3
Inner Join C as c on a.Id    = c.Id
Group By a.Id, a.col1, b.col2

declare @A  table(ID int, col1 varchar(50))
declare @B  table(col2 varchar(50), col3 varchar(50))
declare @C  table(ID int, col4 varchar(50))

INSERT INTO @A(ID, col1) values(1, 'abc')
INSERT INTO @A(ID, col1) values(2, 'bcd')

INSERT INTO @B(col2, col3) values('bcc'  , 'abc')
INSERT INTO @B(col2, col3) values('acc'  , 'bcd')

INSERT INTO @C(ID, col4) values('1'  , 'qwe')
INSERT INTO @C(ID, col4) values('1'  , 'tre')
INSERT INTO @C(ID, col4) values('1'  , 'uid')
INSERT INTO @C(ID, col4) values('2'  , 'jkj')
INSERT INTO @C(ID, col4) values('2'  , 'jwekj')


-- The query
SELECT a.ID, a.col1, b.col2, (SELECT COUNT(c.ID) FROM @C c WHERE c.ID = a.ID) CNT
FROM @A a join @b b ON a.col1 = b.col3

select A.iD, A.Col1,B.col2, 
       (select count(*) from tableC C where C.id=A.ID) as cnt
from tableA A join tableB B on A.col1=b.col3

select A.ID, A.Col1, B.Col2, Count(*) AS Cnt 
from A
inner join B ON B.Col3 = A.Col1
left join C ON C.ID = A.ID
Group By A.ID, A.Col1, B.Col2