在同一列上多次连接两个表，中间有一个查找表

Question

这可能已经得到回答，但是很难搜索这个问题，正如您在我令人困惑的标题中看到的那样。

无论如何，我希望这个例子会有所帮助：

棘手的部分是参数查找表中的一对多关系。

我尝试使用多个连接和别名导致大量行，因为我获得了每个“价格”的每个“金额”。

SELECT paraval.month, paraval.value as amount, paraval2.value as price, trade.position
FROM trade
INNER JOIN parameter para on trade.tID=para.tID and para.name = 'amount'
INNER JOIN parametervalues paraval on para.pID=paraval.pID

INNER JOIN parameter para2 on trade.tID=para2.tID and para2.name = 'price'
INNER JOIN parametervalues paraval2 on para2.pID=paraval2.pID
WHERE trade.type = 'cert'

猜测我需要子查询，但不确定将它们放在哪里。

编辑添加一些 SQL 代码结构：

CREATE TABLE #Trade  
(
    tID             int PRIMARY KEY,  
    type            varchar(50),
    position        int
 );  
CREATE TABLE #Parameter  
(
    pID             int PRIMARY KEY, 
    tID             int, 
    name            varchar(50)
);  
CREATE TABLE #ParameterValue  
(
    pID         int,  
    smonth      varchar(50),
    value       varchar(50));  


INSERT INTO #Trade 
SELECT 1, 'stock', 1
UNION
SELECT 2, 'stock', 2
UNION
SELECT 3, 'cert', 3

INSERT INTO #Parameter 
SELECT 1,1,'amount'
UNION
SELECT 2,1,'price'
UNION
SELECT 3,2,'amount'
UNION
SELECT 4,2,'price'
UNION
SELECT 5,3,'amount'
UNION
SELECT 6,3,'price'

INSERT INTO #ParameterValue
SELECT 1,1,'5'
UNION
SELECT 2,1,'500'
UNION
SELECT 3,1,'15'
UNION 
SELECT 4,1,'300'
UNION
SELECT 5,1,'5'
UNION
SELECT 5,2,'10'
UNION
SELECT 5,3,'5'
UNION
SELECT 6,1,'100'
UNION
SELECT 6,2,'200'
UNION 
SELECT 6,3,'300'

-- SELECT * FROM #Trade

-- SELECT * FROM #Parameter

-- SELECT * FROM #ParameterValue


DROP TABLE #Trade
DROP TABLE #Parameter
DROP TABLE #ParameterValue

Answer 1

我认为构建例外输出和相关模式的最佳方法必须将数据透视表与动态 sql 一起使用，因为在第二天可能会有一些新值，它是结构的主体。

但我认为这个查询可以响应：

SELECT paraval.month, (case when para. name = 'amount' then max(paraval.value) else null end)as amount, (case when para. name = 'price' then  max(paraval.value) else null end) as price, max(trade.position) as position 
FROM trade
INNER JOIN parameter para on trade.tID=para.tID 
INNER JOIN parametervalues paraval on para.pID=paraval.pID
WHERE trade.type = 'cert'
Group by paraval.month 

编辑更正先前的查询：

CREATE TABLE #Trade  
(
    tID             int PRIMARY KEY,  
    type            varchar(50),
    position        int
 );  
CREATE TABLE #Parameter  
(
    pID             int PRIMARY KEY, 
    tID             int, 
    name            varchar(50)
);  
CREATE TABLE #ParameterValue  
(
    pID         int,  
    smonth      varchar(50),
    value       varchar(50));  


INSERT INTO #Trade 
SELECT 1, 'stock', 1
UNION
SELECT 2, 'stock', 2
UNION
SELECT 3, 'cert', 3

INSERT INTO #Parameter 
SELECT 1,1,'amount'
UNION
SELECT 2,1,'price'
UNION
SELECT 3,2,'amount'
UNION
SELECT 4,2,'price'
UNION
SELECT 5,3,'amount'
UNION
SELECT 6,3,'price'

INSERT INTO #ParameterValue
SELECT 1,1,'5'
UNION
SELECT 2,1,'500'
UNION
SELECT 3,1,'15'
UNION 
SELECT 4,1,'300'
UNION
SELECT 5,1,'5'
UNION
SELECT 5,2,'10'
UNION
SELECT 5,3,'5'
UNION
SELECT 6,1,'100'
UNION
SELECT 6,2,'200'
UNION 
SELECT 6,3,'300'


/***/
-- Perform select 
/***/
SELECT t.tID, paraval.smonth, MAX(case when para.name = 'amount' then paraval.value else null end)as amount, MAX(case when para.name = 'price' then  paraval.value else null end) as price, max(T.position) as position 
FROM #Trade T
INNER JOIN #Parameter para on T.tID=para.tID 
INNER JOIN #ParameterValue paraval on para.pID=paraval.pID
Group by T.tId, paraval.smonth
/***/

DROP TABLE #Trade
DROP TABLE #Parameter
DROP TABLE #ParameterValue

结果 ：

tID smonth  amount  price   position
1   1       5       500     1
2   1       15      300     2
3   1       5       100     3
3   2       10      200     3
3   3       5       300     3