Alter Table 更改约束和外键,Case When Then ,联合变换的SQL语句

select *,(case when type=1 then 
    (select typename from TableaType where type=1)
    when type=2 then
    (select typename from TableaType where type=2)
    when type=3 then
    (select typename from TableaType where type=3)
    else 
    (select typename from TableaType where type=4)
    end
) as TypeTmp from Tablea

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select *,(select typename from tableType where type=t.type) as type1 
from tablea t

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--修改表添加主键
ALTER TABLE [tablea] WITH NOCHECK ADD 
     PRIMARY KEY  CLUSTERED 
    (
        [ID]
    )  ON [PRIMARY] 
GO
--修改表添加默认值和唯一约束
ALTER TABLE [tablea] WITH NOCHECK ADD 
  CONSTRAINT [DF__tableb__TypeN__6346339D] DEFAULT ('') FOR [TypeName],
  CONSTRAINT [DF__tableb__TypeR__643A57D6] DEFAULT ('') FOR [TypeRemark],
  CONSTRAINT [UQ__tablea__Type] UNIQUE  NONCLUSTERED 
    (
        [Type]
    )  ON [PRIMARY] 
GO

--修改系表的Type字段添加外键约束到另一个表
ALTER TABLE [tablec] ADD 
    CONSTRAINT [FK_tablec_tablea] FOREIGN KEY 
    (
        [Type]
    ) REFERENCES [tablea] (
        [Type]
    )
GO