Question

假设我有三个名为＆＃34;用户＆＃34;，＆＃34; Bridge＆＃34;和＆＃34;卡＆＃34;：

| ID | FirstName  | LastName |
|----|------------|----------|
| 1  | David      | Gray     |
| 2  | John       | Smith    |

| ID | CardNumber |
|----|------------|
| 1  | 101        |
| 2  | 102        |

| CardNumber | Value |
|------------|-------|
| 101        | ABC   |
| 101        | 1600  |
| 101        | 1700  |
| 101        | 1800  |
| 102        | DEF   |
| 102        | 1699  |
| 102        | 1799  |
| 102        | 1899  |

我正在尝试编写执行以下操作的查询：

从表1中选择 FirstName 和 LastName ，从表2中选择 CardNumber ，从表3中选择值，但我只想为每个用户提供单个最高数字（旁注：我很乐意从卡中获取CardNumber，只要它匹配）

所以我的查询将返回

David, Gray, 101, 1800
John, Smith, 102, 1899

但我无法解决如何在MS-SQL中执行此操作。这是我到目前为止所得到的：

SELECT 
 Users.ID, 
 Users.FirstName, 
 Users.LastName,
 Bridge.CardNumber,
 Cards.Value
FROM Users
 LEFT JOIN Bridge ON Users.ID = Bridge.ID
 LEFT JOIN Cards ON Bridge.CardNumber = Cards.CardNumber
WHERE
 Cards.Value = (SELECT Cards.Value FROM Cards ORDER BY Cards.Value DESC)

返回单个用户，而不是所有用户。删除WHERE子句将返回所有用户，但我不确定如何获得中间地位。

我已经创建了一个SQLite fiddle here，它足够接近（我可以从那里切换口味）

我可以从这里做些什么？

Answer 1

检查这个。使用Group by和max（）函数的简单解决方案。

  SELECT 
   Users.ID, 
   Users.FirstName, 
   Users.LastName,
   Bridge.CardNumber,
   MAX(cast(Cards.Value as int))
  FROM Users
   LEFT JOIN Bridge ON Users.ID = Bridge.Id
   LEFT JOIN Cards ON Bridge.CardNumber = Cards.CardNumber  
  GROUP BY 
   Users.ID, 
   Users.FirstName, 
   Users.LastName,
   Bridge.CardNumber

SQLite fiddle here,

Answer 2

试试这个......

select t1.ID,t1.FirstName,t1.LastName,t2.CardNumber,
max(cast(t3.Value as int)) as [MaxValue] 
from tblUsers t1 
inner join tblBridge t2 on t1.ID=t2.ID
inner join tblCards t3 on t2.CardNumber=t3.CardNumber
where isnumeric(t3.Value)=1    
group by t1.ID,t1.FirstName,t1.LastName,t2.CardNumber

由于连接查询的每次尝试都会从Cards表中计算出最大值并与查询绑定。

Answer 3

试试这个：

select t.*
from (
    select Users.ID,
        Users.FirstName,
        Users.LastName,
        Bridge.CardNumber,
        Cards.Value,
        row_number() over (
            partition by Users.id order by convert(int, Cards.value) desc
            ) rn
    from Users
    left join Bridge on Users.ID = Bridge.ID
    left join Cards on Bridge.CardNumber = Cards.CardNumber
        and Cards.Value not like '%[^0-9]%'
    ) t
where rn = 1;

Answer 4

只需MAX(value)并留在Group BY

<强>架构：

CREATE TABLE #USERS( ID  INT,FirstName   VARCHAR(50),LastName VARCHAR(50))
 INSERT INTO #USERS
SELECT 1,   'David' ,      'Gray'   
UNION ALL  
SELECT 2,   'John'   ,     'Smith'    

CREATE TABLE #BRIDGE( ID INT,  CardNumber VARCHAR(50))
INSERT INTO #BRIDGE

SELECT 1 ,  101        
UNION ALL
SELECT 2 ,  102        

CREATE TABLE #CARDS( CardNumber VARCHAR(50), Value INT)

INSERT INTO #CARDS
SELECT 101,         '1000' 
UNION ALL  
SELECT 101 ,        '1600'  
UNION ALL
SELECT 101 ,        '1700'  
UNION ALL
SELECT 101 ,        '1800'  
UNION ALL
SELECT 102 ,        '800'   
UNION ALL
SELECT 102 ,        '1699'  
UNION ALL
SELECT 102 ,        '1799'  
UNION ALL
SELECT 102 ,        '1899'

根据评论

不，它需要是一个数字，

SELECT U.FirstName, U.LastName, B.CardNumber,MAX( C.Value )
FROM #USERS U
INNER JOIN #BRIDGE B ON U.ID = B.ID
INNER JOIN #CARDS C ON B.CardNumber = C.CardNumber
GROUP BY  U.FirstName, U.LastName, B.CardNumber

如果Value的类型为varchar并且具有类似ABC的值，并且您想要排除它们。

SELECT U.FirstName, U.LastName, B.CardNumber,MAX(CAST( C.Value AS INT)  )
FROM #USERS U
INNER JOIN #BRIDGE B ON U.ID = B.ID
INNER JOIN #CARDS C ON B.CardNumber = C.CardNumber
WHERE ISNUMERIC(Value)=1
GROUP BY  U.FirstName, U.LastName, B.CardNumber

结果将是

+-----------+----------+------------+-------+
| FirstName | LastName | CardNumber | value |
+-----------+----------+------------+-------+
| David     | Gray     |        101 |  1800 |
| John      | Smith    |        102 |  1899 |
+-----------+----------+------------+-------+

Answer 5

使用简单的子查询我们也可以这样做

select 
T.FirstName, 
T.LastName,
TT.CardNumber,
TTT.Value 
    from  users T
INNER JOIN Bridge TT
ON T.ID = TT.ID
INNER JOIN (Select MAX(Value) Value ,
                CardNumber 
                            from  Cards 
                                WHERE CardNumber = CardNumber
AND VALUE  LIKE  '%[^A-Za-z]%'
GROUP BY CardNumber) TTT
ON TT.CardNumber = TTT.CardNumber

Answer 6

使用LEFT JOIN。并根据Cards列为Value表格提供行号。

<强>查询

select t1.FirstName, t1.LastName, t2.CardNumber, t3.Value
from Users t1
left join Bridge t2
on t1.ID = t2.ID
left join (
    select [rn] = row_number() over(
        partition by CardNumber 
        order by case when Value like '[0-9]%' then 1 else 2 end,
        len(Value) desc, Value desc
    ), * from Cards) t3
on t2.CardNumber = t3.CardNumber
and t3.[rn] = 1;

从两个表中提取所有数据，从第三个表中单行？

6 个答案: