if (exists (select * from information_schema.columns where table_name = 'student' and column_name = 'tel')) alter table student drop column tel go ▓▓ 添加、删除约束 --添加新列、约束 alter table student add number varchar(20) null constraint no_uk unique; --增加主键 alter table student...
ALTER TABLE student ADD CONSTRAINT FK_student_class FOREIGN KEY(classid) REFERENCES class(id) ON DELETE set null; IF EXISTS(SELECT * FROM sys.tables WHERE name = N'book') DROP table book; GO create table book( id int not null, name varchar(50) not null ); go ALTER TABLE book ADD ...
foreign key(stuNo) references stuInfo(stuNo) alter table stuMarks --指定表名 drop constraint fk_stuNo --指定删除的约束名 constraint 只是显示和隐式的区别,删除外键约束 ---建立用户--- use stuDB ---zhuheDBUser为数据库用户名--- exec sp_grantdbaccess 'zhuhe-PC\SQLServer2005MSFTEUser$ZHUHE...
ifexists(select*fromsysobjectswherename='T_product_review')begin...endelsebegincreatetableT_product_review ( ... )endgo 2.3 给表添加约束 1.default --给三个表的register_date设置一个默认值,提交时间为当前时间altertableT_productaddconstraintregistertimedefault(getdate())forregister_datealtertableT_cate...
改進最佳化SQL Server 2022 (16.x) 利用新的硬體功能 (包括 Advanced Vector Extension (AVX) 512 延伸項目) 改善批次模式作業。 需要追蹤旗標 15097。 請參閱DBCC TRACEON - 追蹤旗標 (Transact-SQL)。 語言 新功能或更新詳細資料 可恢復的新增資料表約束條件支援暫停與繼續執行 ALTER TABLE ADD CONSTRAINT的...
當 SQL Server 嘗試存取還未出現在緩衝集區中的頁面時,會公佈非同步的 I/O,將頁面載入緩衝集區。 如果 SQL Server 必須等候 I/O 子系統的回應,其會等待獨佔 (PAGEIOLATCH_EX) 或共用 (PAGEIOLATCH_SH) I/O 閂鎖,視要求的類型而定;這是為了防止另一個背景工作執行緒將相同的頁面載入具有不相容閂鎖的緩衝集...
If the DELETE removes multiple rows, and any one of the removed rows violates a trigger or constraint, the statement is canceled, an error is returned, and no rows are removed.When a DELETE statement encounters an arithmetic error (overflow, divide by zero, or a domain error) occurring ...
If the DELETE removes multiple rows, and any one of the removed rows violates a trigger or constraint, the statement is canceled, an error is returned, and no rows are removed.When a DELETE statement encounters an arithmetic error (overflow, divide by zero, or a domain error) occurring ...
If the DELETE removes multiple rows, and any one of the removed rows violates a trigger or constraint, the statement is canceled, an error is returned, and no rows are removed.When a DELETE statement encounters an arithmetic error (overflow, divide by zero, or a domain error) occurring ...
SQL Server通过ghost-cleanup线程来删除虚影记录。但删除的时机却无法预料,DELETE操作不会影响ghost-cleanup的行为,但会将新的虚影记录加到待删除的虚影记录队列末尾,而这个线程定期清理这些记录 ghost-cleanup线程大概每5秒被唤醒一次,每次唤醒大概清理10页虚影记录,这个值会随着SQL Server版本的不同而不同 ...