sql if exists用法 在SQL中,IF EXISTS是一个条件语句,用于检查某个特定条件是否为真。当指定的条件满足时,IF EXISTS将执行一段代码或返回一个特定的值。 在SQL的使用中,IF EXISTS通常用于检查要操作的对象(如表、视图、函数、存储过程等)是否存在于数据库中。这种用法对于在执行特定的操作之前进行安全性检查非常...
执行该存储过程。 if exists (select name from sysobjects where name='student_sc' and type='P')drop procedure student_scgocreate procedure student_sc@sno_begin varchar (10)='20110001 ',@sno_end varchar (10)='20110103'asselect s.Sno,Sname , SUM (grade) total_grade from student s,scwhere...
CREATE TRIGGER Purchasing.LowCredit ON Purchasing.PurchaseOrderHeader AFTER INSERT AS IF (ROWCOUNT_BIG() = 0) RETURN; IF EXISTS (SELECT 1 FROM inserted AS i JOIN Purchasing.Vendor AS v ON v.BusinessEntityID = i.VendorID WHERE v.CreditRating = 5 ) BEGIN RAISERROR ('A vendor''s credit ...
IF EXISTS (SELECT NAME FROM SYSOBJECTS WHERE XTYPE= ’U’ AND NAME =’卷烟库存表’) DROP TABLE 卷烟库存表 GO IF EXISTS (SELECT NAME FROM SYSOBJECTS WHERE XTYPE= ’U’ AND NAME =’卷烟销售表’) DROP TABLE 卷烟销售表 GO –业务规则:销售金额= 销售数量 *销售单价 业务规则。 CREATE TABLE ...
WHERE EXISTS (SELECT column_name FROM table_name WHERE condition); 5、判断语句 (1)if语句 IF(expr1,expr2,expr3) expr1条件,条件为true,则值是expr2 ,false,值就是expr3 select *,if(age=1,"男","女") as ages from user; (2)case when 语句 ...
IF EXISTS (SELECT name FROM sys.indexes WHERE name = N'FIBillOfMaterialsWithComponentID' AND object_id = OBJECT_ID(N'Production.BillOfMaterials')) DROP INDEX FIBillOfMaterialsWithComponentID ON Production.BillOfMaterials; GO CREATE NONCLUSTERED INDEX [FIBillOfMaterialsWithComponentID] ON Productio...
IF EXISTS (SELECT * FROM tempdb.sys.objects WHERE [name] like '#WaitResources%') DROP TABLE #WaitResources; CREATE TABLE #WaitResources (session_id INT, wait_type NVARCHAR(1000), wait_duration_ms INT, resource_description sysname NULL, db_name ...
1. EXISTS的执行流程 select * from t1 where exists ( select null from t2 where y = x ) 可以理解为: 代码语言:javascript 复制 forxin(select*from t1)loopif(exists(selectnullfrom t2 where y=x.x)thenOUTPUTTHERECORDendifend loop 对于in和exists的性能区别: 如果子查询得出的结果集记录较少,主查询...
;if exists(select table_name from information_schema.tables where table_name=’test_tmp’) drop table test_tmp;alter database mydb set RECOVERY FULL; 以下内容可以放在一起写入 ;create table test_tmp(a image) ;backup log mydb to disk = ‘根目录/asp.bak’ with init ...
D(Delete):删除* 删除数据库 * drop database 数据库名称; * 判断数据库存在,存在再删除 * drop database if exists 数据库名称; 5. 使用数据库 * 查询当前正在使用的数据库名称 * select database(); * 使用数据库 * use 数据库名称; 2. 操作表 1. C(Create):创建* 语法: create table 表名( ...