T-SQL：使用多个连接的相同字段

Question

我查看了类似的问题，但找不到特定问题的答案。我正在使用 SQL Server 2008（SQL Server Management Studio 中的 T-SQL）（但更习惯于 Oracle 和 Crystal Reports）。

简化场景：

表客户

customerID (pk)...

表格InsuranceCoverage

customerID (composite pk)
line (composite pk)
insCompanyID (fk)
insPlanID (fk)

表格InsuranceCompany

insCompanyID
insCompanyName
insCompanyAddr

表格InsurancePlan

insPlanID
insPlanName
insPlanClass

我需要一份基本上在一行上返回以下内容的报告：

1. 来自Customer 的几列
2. Insurance 1 - InsuranceCompany 和 InsurancePlan 表中 InsuranceCoverage.line = 1 的列
3. Insurance 2 - InsuranceCompany 和 InsurancePlan 表中 InsuranceCoverage.line = 2 的列
4. Insurance 3 - InsuranceCompany 和 InsurancePlan 表中 InsuranceCoverage.line = 3 的列

我觉得自己很愚蠢，无法弄清楚这一点。一位客户最多可能拥有三份保险。这很容易为其编写多个查询，但我必须对其进行设置，以便它可以每月自动运行 1 次。我之前通过在连接上使用别名在同一个报告中多次使用同一个表，但是由于 InsuranceCoverage.line 标准，这在这里不起作用，对吧？ from 子句中的子查询是答案吗？

Answer 1

这样的？

SELECT
    c.CustomerID,
    cov1.*,
    cov2.*,
    cov3.*,
    insco1.insCompanyName as insCompanyName1,
    insco2.insCompanyName as insCompanyName2,
    insco3.insCompanyName as insCompanyName3,
    etc...
FROM
    Customer c
    LEFT OUTER JOIN InsuranceCoverage cov1 on cov1.CustomerID = c.CustomerID AND cov1.line = 1
    LEFT OUTER JOIN InsuranceCoverage cov2 on cov2.CustomerID = c.CustomerID AND cov2.line = 2
    LEFT OUTER JOIN InsuranceCoverage cov3 on cov3.CustomerID = c.CustomerID AND cov3.line = 3
    JOIN InsuranceCompany insco1 on insco1.insCompanyID = cov1.insCompanyID
    JOIN InsuranceCompany insco2 on insco2.insCompanyID = cov2.insCompanyID
    JOIN InsuranceCompany insco3 on insco3.insCompanyID = cov3.insCompanyID
    JOIN InsurancePlan inspl1 on inspl1.insPlanID = cov1.insPlanID
    JOIN InsurancePlan inspl2 on inspl2.insPlanID = cov2.insPlanID
    JOIN InsurancePlan inspl3 on inspl3.insPlanID = cov3.insPlanID

Answer 2

我设置了一些表变量以显示此查询有效。您需要将它们替换为真实的表名和列名。我相信这样的事情会为你工作：

DECLARE @Customer TABLE (CustomerId INT)

DECLARE @InsuranceCoverage TABLE
(
    CustomerId INT
    , Line INT
    , InsuranceCompanyId INT
    , InsurancePlanId INT
)

DECLARE @InsuranceCompany TABLE
(
    Id INT
    , Name VARCHAR(100)
    , Addr VARCHAR(100)
)

DECLARE @InsurancePlan TABLE
(
    Id INT
    , Name VARCHAR(100)
    , Class VARCHAR(100)
)

SELECT
    C.* -- Customer colums.
    -- Insurance1 columns.
    , ICmp1.*
    , IP1.*
    -- Insurance2 columns.
    , ICmp2.*
    , IP2.*
    -- Insurance3 columns.
    , ICmp3.*
    , IP3.*
    FROM
    @Customer C
    LEFT JOIN @InsuranceCoverage ICov1          
        INNER JOIN @InsuranceCompany ICmp1
            ON ICmp1.Id = ICov1.InsuranceCompanyId
        INNER JOIN @InsurancePlan IP1
            ON IP1.Id = ICov1.InsurancePlanId
        ON ICov1.CustomerId = C.CustomerId
        AND ICov1.Line = 1
    LEFT JOIN @InsuranceCoverage ICov2
        INNER JOIN @InsuranceCompany ICmp2
            ON ICmp2.Id = ICov2.InsuranceCompanyId
        INNER JOIN @InsurancePlan IP2
            ON IP2.Id = ICov2.InsurancePlanId
        ON ICov2.CustomerId = C.CustomerId
        AND ICov2.Line = 2
    LEFT JOIN @InsuranceCoverage ICov3
        INNER JOIN @InsuranceCompany ICmp3
            ON ICmp3.Id = ICov3.InsuranceCompanyId
        INNER JOIN @InsurancePlan IP3
            ON IP3.Id = ICov3.InsurancePlanId
        ON ICov3.CustomerId = C.CustomerId
        AND ICov3.Line = 3

Answer 3

您可以将 2、3、4 合并为派生表，然后将 1 与它连接起来，例如...

select t1.a,t1.b,t1.c, t2.d, t2.e, t2.f from customer t1, 
(select fk, d as d, 0 as e, 0 as f from ic where line=1
  union select fk, 0, e, 0 from ic where line=2
  union select fk, 0, 0, f from ic where line=3) as t2
where t1.pk = t2. fk

类似的东西

编辑：哦，对了，如果他们没有保险，那就把它改成左连接，比如......

select t1.a,t1.b,t1.c, t2.d, t2.e, t2.f from customer t1 left join  
(select fk, d as d, 0 as e, 0 as f from ic where line=1
  union select fk, 0, e, 0 from ic where line=2
  union select fk, 0, 0, f from ic where line=3) as t2
 on t1.pk = t2.fk

...或类似的东西:)