Sql 查询的麻烦

我有一个表

TContractForm

，表中有

idcontract（主键）、idcntrtype（外键）、date\u begin、date\u end、cost

字段。我还有三种合同：

TrenthouseContract

带有字段

idcontract、idclient、idpdtwhs

TRentShoppointContract

带有字段

idcontract、idclient、idshoppoint、idshoptype

TRentEquipContract

带字段

idcontract、idclient、ideq、amount

idcntrtype

-合同类型

t合同类型

-

idcntrtype（主键）、idcntrclass（外键）、name

<代码>合同类-

idcntrclass，名称

我想创建一个包含列的视图

idcontract、idclient、合同类型（类型名称）、合同类别（类别名称）、开始日期、结束日期、成本

但我的查询没有返回任何内容（我知道TRentWhouseContract表中有几个契约（其他表没有行）（它没有idclient，因为如果某个表为空，我不知道如何从不同的表中获取相同的idclient）

如何获取idclient：

coalesce(TREC.idclient, TRSPC.idclient,TRWC.idclient) as idclient

Coalesce返回第一个非缺失值

至于其余的-我认为您应该做左外部连接而不是逗号连接，因为您没有在所有表中都有一些记录（嗯，所有表中都没有记录！）

等等。

如何获取idclient：

coalesce(TREC.idclient, TRSPC.idclient,TRWC.idclient) as idclient

Coalesce返回第一个非缺失值

至于其余的-我认为您应该做左外部连接而不是逗号连接，因为您没有在所有表中都有一些记录（嗯，所有表中都没有记录！）

---

等等。

如果我理解正确，我会这样做

select TCF.idcontract,
   --idclient
   TCF.date_begin,
   TCF.date_end,
   TCT.name as [type],
   TCC.name as class,
   TCF.cost
from TContractForm as TCF
JOIN TContractType as TCT
   ON TCT.idcntrtype=TCF.idcntrtype
JOIN TContractClass as TCC
   ON TCT.idcntrclass = TCC.idcntrclass
UNION
select TCF.idcontract,
   --idclient
   TCF.date_begin,
   TCF.date_end,
   TCT.name as [type],
   TCC.name as class,
   TCF.cost
from TRentWhouseContract as TCF
JOIN TContractType as TCT
   ON TCT.idcntrtype=TCF.idcntrtype
JOIN TContractClass as TCC
   ON TCT.idcntrclass = TCC.idcntrclass
UNION
select TCF.idcontract,
   --idclient
   TCF.date_begin,
   TCF.date_end,
   TCT.name as [type],
   TCC.name as class,
   TCF.cost
from TRentShoppointContract as TCF
JOIN TContractType as TCT
   ON TCT.idcntrtype=TCF.idcntrtype
JOIN TContractClass as TCC
   ON TCT.idcntrclass = TCC.idcntrclass
UNION
select TCF.idcontract,
   --idclient
   TCF.date_begin,
   TCF.date_end,
   TCT.name as [type],
   TCC.name as class,
   TCF.cost
from TRentEquipContract as TCF
JOIN TContractType as TCT
   ON TCT.idcntrtype=TCF.idcntrtype
JOIN TContractClass as TCC
   ON TCT.idcntrclass = TCC.idcntrclass

---

如果我理解正确，我会这么做

select TCF.idcontract,
   --idclient
   TCF.date_begin,
   TCF.date_end,
   TCT.name as [type],
   TCC.name as class,
   TCF.cost
from TContractForm as TCF
JOIN TContractType as TCT
   ON TCT.idcntrtype=TCF.idcntrtype
JOIN TContractClass as TCC
   ON TCT.idcntrclass = TCC.idcntrclass
UNION
select TCF.idcontract,
   --idclient
   TCF.date_begin,
   TCF.date_end,
   TCT.name as [type],
   TCC.name as class,
   TCF.cost
from TRentWhouseContract as TCF
JOIN TContractType as TCT
   ON TCT.idcntrtype=TCF.idcntrtype
JOIN TContractClass as TCC
   ON TCT.idcntrclass = TCC.idcntrclass
UNION
select TCF.idcontract,
   --idclient
   TCF.date_begin,
   TCF.date_end,
   TCT.name as [type],
   TCC.name as class,
   TCF.cost
from TRentShoppointContract as TCF
JOIN TContractType as TCT
   ON TCT.idcntrtype=TCF.idcntrtype
JOIN TContractClass as TCC
   ON TCT.idcntrclass = TCC.idcntrclass
UNION
select TCF.idcontract,
   --idclient
   TCF.date_begin,
   TCF.date_end,
   TCT.name as [type],
   TCC.name as class,
   TCF.cost
from TRentEquipContract as TCF
JOIN TContractType as TCT
   ON TCT.idcntrtype=TCF.idcntrtype
JOIN TContractClass as TCC
   ON TCT.idcntrclass = TCC.idcntrclass

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我应该使用

合并

内部

选择

？我应该使用

合并

内部

选择

？