sql server 中有哪几种约束?

一共有六种约束:这里以学生表stuinfo为例

1、添加主键约束alter table stuinfo add costraint pk_stuno primary key (stuno)

2、2、唯一约束alter table stuinfo add constraint uq_stuid unique (stuid)

3、3、添加默认约束alter table stuinfo add constraint df_address default ('地址不详') for address

4、4、添加检查约束alter table stuinfo add constraint ck_age check (age between 15 and 40) 这是年龄在15到40之间

5、5、添加外键约束alter table stumarks add constraint fk_stuno foreign key (stuno) references stuinfo (stuno)这是一个成绩表(stumarks)引用学生信息表中的列 学号

6、6、not null 非空约束，强制不接受空值，例如，创建表时，name varchar(6) not null

--创建约束
--为性别增加一个检查约束，要求性别只能是：'男' or '女'
alter table AbcTable add constraint CK_AbcTable_EmpGender check(EmpGender='男' or EmpGender='女')
--删除单个约束
alter table AbcTable drop constraint CK_AbcTable_EmpGender
--为EmpName增加一个唯一约束
alter table Employees add constraint UQ_Employees_EmpName unique(EmpName)

--为订单增加检查约束,要求Payment=(PaymentToBId+PaymentToTm)
alter table Trade add constraint CK_Trade_PaymentLargeZero check(Payment>0 and PaymentToBid>0)
alter table Trade add constraint CK_Trade_PaymentToBidToTm check(Payment=(PaymentToBid+PaymentToTm))
alter table [Order] add constraint CK_Order_PaymentToBidToTm check(Payment=(PaymentToBid+PaymentToTm))
alter table ChannelInMoneyFlow add constraint UQ_ChannelInMoneyFlow_InTradePayDate unique(InTradePayDate)

--查找Check约束
select * from sys.check_constraints chk
select * from sys.tables tab

SELECT
  tab.name AS [表名],
  chk.name AS [Check约束名],
  chk.definition
FROM
  sys.check_constraints chk
    JOIN sys.tables tab
      ON (chk.parent_object_id = tab.object_id)

----查找唯一约束
select * from sys.indexes idx where idx.is_unique_constraint = 1

SELECT
  tab.name AS [表名],
  idx.name AS [约束名称],
  col.name AS [约束列名]
FROM
  sys.indexes idx
    JOIN sys.index_columns idxCol
      ON (idx.object_id = idxCol.object_id
          AND idx.index_id = idxCol.index_id
          AND idx.is_unique_constraint = 1)
    JOIN sys.tables tab
      ON (idx.object_id = tab.object_id)
    JOIN sys.columns col
      ON (idx.object_id = col.object_id
          AND idxCol.column_id = col.column_id);

----查找外键约束
select * from sys.foreign_keys fk 

select
  oSub.name  AS  [子表名称],
  fk.name AS  [外键名称],
  SubCol.name AS [子表列名],
  oMain.name  AS  [主表名称],
  MainCol.name AS [主表列名]
from
  sys.foreign_keys fk 
    JOIN sys.all_objects oSub 
        ON (fk.parent_object_id = oSub.object_id)
    JOIN sys.all_objects oMain
        ON (fk.referenced_object_id = oMain.object_id)
    JOIN sys.foreign_key_columns fkCols
        ON (fk.object_id = fkCols.constraint_object_id)
    JOIN sys.columns SubCol
        ON (oSub.object_id = SubCol.object_id 
            AND fkCols.parent_column_id = SubCol.column_id)
    JOIN sys.columns MainCol
        ON (oMain.object_id = MainCol.object_id 
            AND fkCols.referenced_column_id = MainCol.column_id)

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