动态SQL JOIN而不是UNION

我目前有多个下面的查询（实际代码的小片段），我多次执行UNION ALL SELECT，因为订单可能有1到5个与之相关的贷款。但是，我想知道如何动态引入LoanOrder（如果可能），我不会使用UNION ALL并只调整LoanOrder？这样，如果实际上只有一个与订单关联的贷款，我不会再运行两个额外的SELECT报表。虽然我目前的方法有效，但我只是试图更好地优化并为我未来的工作学习新东西。提前致谢！动态SQL JOIN而不是UNION

SELECT DISTINCT 
    -- 1st Loan Premiums 
    L.LoanOrder 
    ,'Loan Premium' AS 'Type' 
    ,'Policies:' AS 'Type1' 
FROM 
    Orders O 
    LEFT JOIN Loan L 
     ON O.OrdersID = L.OrdersID 
     AND L.LoanOrder = 1 
UNION ALL 
SELECT DISTINCT 
    -- 2nd Loan Premiums 
    L.LoanOrder 
    ,'Loan Premium' AS 'Type' 
    ,'Policies:' AS 'Type1' 
FROM 
    Orders O 
    LEFT JOIN Loan L 
     ON O.OrdersID = L.OrdersID 
     AND L.LoanOrder = 2 
UNION ALL 
SELECT DISTINCT 
    -- 3rd Loan Premiums 
    L.LoanOrder 
    ,'Loan Premium' AS 'Type' 
    ,'Policies:' AS 'Type1' 
FROM 
    Orders O 
    LEFT JOIN Loan L 
     ON O.OrdersID = L.OrdersID 
     AND L.LoanOrder = 3 
UNION ALL 
SELECT DISTINCT 
    -- 4th Loan Premiums 
    L.LoanOrder 
    ,'Loan Premium' AS 'Type' 
    ,'Policies:' AS 'Type1' 
FROM 
    Orders O 
    LEFT JOIN Loan L 
     ON O.OrdersID = L.OrdersID 
     AND L.LoanOrder = 4 
UNION ALL 
SELECT DISTINCT 
    -- 5th Loan Premiums 
    L.LoanOrder 
    ,'Loan Premium' AS 'Type' 
    ,'Policies:' AS 'Type1' 
FROM 
    Orders O 
    LEFT JOIN Loan L 
     ON O.OrdersID = L.OrdersID 
     AND L.LoanOrder = 5

来源

2015-03-30 PicoDeGallo

好像改变是L.LoadOrder =＃唯一;也许我不明白这个问题，但你不能只写： 'SELECT DISTINCT LoanOrder，'Loan Premium'，'Policies'FROM Orders O LEFT JOIN Loan L ON（O.OrdersID = L.OrdersID AND L .LoanOrder IN（1，2，3，4，5））' 这将为您带来所有订单，并在贷款订单介于1和5之间（包括1和5）的贷款表上存在匹配记录。 – 2015-03-30 18:11:36

此外，如果你只想要订单有贷款的地方，添加以下WHERE子句： ' WHERE L.OrdersID不是NULL' – 2015-03-30 18:15:01

哇，我甚至没有关于使用'IN'运算符。这正是我需要做的，并且不需要多个'UNION'语句。这次真是万分感谢！我会回到现在感觉像个傻瓜。 :) @Kalmino – PicoDeGallo 2015-03-30 18:19:24

您似乎根本没有使用Orders表。所以，我觉得您的查询的一个简化版本是：

SELECT L.LoanOrder, 'Loan Premium' AS 'Type', 'Policies:' AS 'Type1' 
FROM Loan L 
WHERE L.LoanOrder IN (1, 2, 3, 4, 5);

您可能使用orders过滤，但似乎不太可能。

我也删除了distinct - 理由是这可能是不必要的。如果一个LoanOrder可以出现在Loan的多行上，那么您可能需要它。

编辑：

如果确实需要Orders：

SELECT DISTINCT L.LoanOrder, 'Loan Premium' AS 'Type', 'Policies:' AS 'Type1' 
FROM Orders o LEFT JOIN 
    Loan L 
    ON O.OrdersID = L.OrdersID AND 
     L.LoanOrder IN (1, 2, 3, 4, 5);

来源

2015-03-30 18:21:13

在完整的查询中，我实际上使用了'Orders'表，我刚刚提供了一个查询的小片段。无论如何，“IN”运算符正是我需要完成的。谢谢！ – PicoDeGallo 2015-03-30 18:22:25

这有什么错

SELECT DISTINCT 
    L.LoanOrder 
    ,'Loan Premium' AS 'Type' 
    ,'Policies:' AS 'Type1' 
FROM 
    Orders O 
    LEFT JOIN Loan 
    ON O.OrdersID = L.OrdersID 
     AND L.LoanOrder > 0 
     AND L.LoanOrder < 6

？

来源

2015-03-30 18:15:13

动态SQL JOIN而不是UNION

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