SQL級聯更新和級聯刪除

alter table 表名
add constraint 約束名
foreign key(字段名) references 主表名(字段名)
on delete cascade

語法：
Foreign Key
(column[,...n])
references referenced_table_name[(ref_column[,...n])]
[on delete cascade]
[on update cascade]
註釋：
column:列名
referenced_table_name:外鍵參考的主鍵表名稱
ref_name:外鍵要參考的表的主鍵列
on delete:刪除級聯
on update:更新級聯

表的外鍵約束

SELECT 外鍵表ID=b.fkeyid
,外鍵表名稱=object_name(b.fkeyid)
,外鍵列ID=b.fkey
,外鍵列名=(SELECT name FROM syscolumns WHERE colid=b.fkey AND id=b.fkeyid)
,主鍵表ID=b.rkeyid
,主鍵表名=object_name(b.rkeyid)
,主鍵列ID=b.rkey
,主鍵列名=(SELECT name FROM syscolumns WHERE colid=b.rkey AND id=b.rkeyid)
FROM sysobjects a
join sysforeignkeys b on a.id=b.constid
join sysobjects c on a.parent_obj=c.id
where a.xtype='f' AND c.xtype='U'   
    
    
    
查詢一個表的所有外鍵:

SELECT 主鍵列ID=b.rkey
,主鍵列名=(SELECT name FROM syscolumns WHERE colid=b.rkey AND id=b.rkeyid)
,外鍵表ID=b.fkeyid
,外鍵表名稱=object_name(b.fkeyid)
,外鍵列ID=b.fkey
,外鍵列名=(SELECT name FROM syscolumns WHERE colid=b.fkey AND id=b.fkeyid)
FROM sysobjects a
join sysforeignkeys b on a.id=b.constid
join sysobjects c on a.parent_obj=c.id
where a.xtype='f' AND c.xtype='U'
and object_name(b.rkeyid)='要查詢的表名'