SQL集检查约束

我在设置“检查约束”时遇到问题。我有一个表Policy，其中主键设置在Policy\u id、History\u id+附加列上，表Report有Policy\u id和一些附加列

如何在报表表上设置check constraint语句以检查策略表中是否存在策略id

我无法使用外键约束，因为报表没有“历史记录\u id”列

如果策略表中不存在具有策略id的记录，则报表不能包含该记录，因此无法执行插入到报表中

如果策略id和历史id是复合主键，则引用表上的外键也必须同时包含这两列

如果你真的只需要检查其中一个策略id，我想你必须手动执行，这不是一个好主意

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如果报表表有2个外键，并且策略id和历史id都是一个主键，则效果更好。

您可以仅为该外键约束的目的创建一个单独的表，然后使用触发器来维护该数据：

CREATE TABLE ExistingPolicies (
    PolicyID int not null,
    PolicyCount int not null,
    constraint PK_ExistingPolicies PRIMARY KEY (PolicyID)

然后触发：

CREATE TRIGGER T_Policy_I
on Policy
instead of insert
as
     ;With totals as (
         select PolicyID,COUNT(*) as cnt from inserted
         group by PolicyID
     )
     merge into ExistingPolicies t
     using totals s
     on
        t.PolicyID = s.PolicyID
     when matched then update set PolicyCount = PolicyCount + s.cnt
     when not matched then insert (PolicyID,PolicyCount) values (s.PolicyID,s.cnt);
go
CREATE TRIGGER T_Policy_D
on Policy
instead of delete
as
     ;With totals as (
         select PolicyID,COUNT(*) as cnt from deleted
         group by PolicyID
     )
     merge into ExistingPolicies t
     using totals s
     on
        t.PolicyID = s.PolicyID
     when matched and t.PolicyCount = s.cnt then delete
     when matched then update set PolicyCount = PolicyCount - s.cnt;
go
CREATE TRIGGER T_Policy_U
on Policy
instead of update
as
     ;With totals as (
         select PolicyID,SUM(cnt) as cnt
         from
            (select PolicyID,1 as cnt from inserted
             union all
             select PolicyID,-1 as cnt from deleted
             ) t
         group by PolicyID
     )
     merge into ExistingPolicies t
     using totals s
     on
        t.PolicyID = s.PolicyID
     when matched and t.PolicyCount = -s.cnt then delete
     when matched then update set PolicyCount = PolicyCount + s.cnt
     when not matched then insert (PolicyID,PolicyCount) values (s.PolicyID,s.cnt);
go

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代码未经测试，但应该接近正确

我认为在这里使用检查约束是一个好主意

编写一个函数，接受Policy_id作为参数，并执行查询以检查Policy表中是否存在该策略，并返回一个简单的1 exists或0 notexists

然后将报表表上的检查约束设置为dbo.MyFunctionPolicy\u Id=1

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就是这样。

您可以编写一个函数，接受策略id并检查它是否存在于策略表中。