判断table1中是否存在name字段 if exists(select * from syscolumns whereid=object_id('table1') andname='name') begin select * from people; end 判断table1中是否存在name字段且删除字段 if exists(select * from syscolumns whereid=object_id('table1') andname='name') begin select * from people;...
N'IsUserTable')=1)BEGINdropTABLEtbnameEND--存储过程IFexists(SELECT1fromsys. sysobjectswhereid=object_id(N'System_GetTableCreateSql')ANDOBJECTPROPERTY(id, N'IsProcedure')=1)BEGINdropPROC
SELECT @tableName = N'' WHILE EXISTS (SELECT * FROM #tables WHERE tableName > @tableName) BEGIN SELECT @tableName = MIN(tableName) FROM #tables WHERE tableName > @tableName SELECT @sql = 'EXEC ' + @SourceDB + '..SP_EXECUTESQL N''INSERT #SpaceUsed EXEC SP_SPACEUSED [' + @table...
private Button btn = new Button(); private void Form1_Load(object sender, EventArgs e) ...
IF EXISTS(SELECT name FROM sys.sysobjects WHERE Name = N'table_name' AND xtype = N'U') BEGIN PRINT 'Table Exists...' END ELSE BEGIN PRINT 'Table Does not Exists...' END SQL Puzzle: SQL Advance Query - Do basic validation of Email AddressPostgreSQL: Optimize the Function by defining...
1 CREATE DATABASE 句法 2 3 CREATE DATABASE [IF NOT EXISTS] db_name 4 5 ...
(5,'赵涛');DROPTABLEIFEXISTSstudent_info_2;CREATETABLEstudent_info_2(student_idINT(8),student_nameVARCHAR(8))ENGINE=InnoDBDEFAULTCHARSET=utf8;INSERTINTOstudent_info_2(student_id,student_name)VALUE(1,'李明'),(2,'王猛'),(3,'吴丽丽'),(4,'张飞');-- 数据表内容:select*fromstudent_info_...
这次介绍一下T-SQL中“Not IN” 和“Not Exists”的优化。 Not IN 和 Not Exists 命令 : 有些情况下,需要select/update/delete 操作孤立数据。孤立数据:不存在主表中而存在其关联表中。 操作这样的数据,一般第一反应是利用“Not in” 或“Not Exists”命令。使用Not IN会严重影响性能,因为这个命令会逐一检查...
if exists(select * from sysobjects where name='Teacher') drop table Teacher go create table Teacher ( -- TeacherId int primary key, --讲师编号,主键 TeacherId int identity(100,1) primary key,--自增主键用identity(基数,增量) LoginAccount varchar(50) not null,--登录帐号 ...
子查询[AS] table_alias。 有关详细信息,请参阅FROM (Transact-SQL)。 适用于: SQL Server 2016 (13.x)。从 SQL Server 2016 (13.x) 开始,本机编译模块已支持子查询。 WHERE 子句: 筛选器谓词 IS [NOT] NULL AND、BETWEEN OR、NOT、IN、EXISTS ...