IF EXISTS语法:IF EXISTS (SELECT * FROM information_schema.tables WHERE table_schema = 'database_name' AND table_name = 'table_name')THEN SQL_statement; END IF; 其中,database_name是数据库的名称,table_name是表的名称,SQL_st
IF(EXISTS(SELECT 1 FROM table_name WHERE condition),true_statement, false_statement) 这个函数接受一个子查询作为参数,并根据子查询的结果返回相应的值。如果子查询返回的结果集不为空,则IF EXISTS函数返回true_statement;如果子查询返回的结果集为空,则返回false_statement。 下面是一个更具体的实例,以帮助我们...
之所以叫它CASE“表达式”而不是CASE“语句”(statement),是因为CASE表达式与1+(2-4)或者(x*y)/z一样,都是表达式,在执行时会被整体当作一个值来处理。既然同样是表达式,那么能写1+1这样的表达式的地方就都能写CASE表达式,而且因为CASE表达式最终会作为一个确定的值来处理,所以我们也可以把CASE表达式当作聚合函数...
[…n ]|IF ( COLUMNS_UPDATED ( ) { bitwise_operator } updated_bitmask ) { comparison_operator } column_bitmask [ …n ] } ] sql_statement [ …n ] } }4、关于触发器,还应该注意 (1)、DELETE 触发器不能捕获 TRUNCATE TABLE 语句。 (2)、触发器中不允许以下 Transact-SQL 语句: ALTER DATABA...
Vibhore, While it is true that the update statement is doing nothing if you are just doing inserts, it is no less performant that using if (exists). In the case of an insert, both will perform one table scan (or index search) to perform the insert. In the case of Update first, it...
If the record exists, it is updated, else inserted. http://dev.mysql.com/doc/refman/5.0/en/replace.html Anonymous February 21, 2008 The comment has been removed Anonymous February 21, 2008 Looking into the MySql documentation a little more I found this statement: INSERT ... ON DUPLICATE ...
T-SQL – Select Top 1 and If Not Exist Return Null Row IF EXISTS ( SELECT * FROM [dbo].[PLAYER] WHERE [PLAYER_ID] = @player_id ) SELECT TOP 1 [PLAYER_ID], [PLAYER_NAME], [PLAYER_NATION], [PLAYER_TEAM], [PLAYER_BIRTHDAY] ...
1 if (exists (select * from sys.objects where name = 'proc_get_student')) drop proc proc_get_studentgocreate proc proc_get_studentas select * from student;--调用、执行存储过程exec proc_get_student;3、 修改存储过程 1 alter proc proc_get_studentasselect * from student;4、...
MySQL SQL Statement 官方测试数据:https://dev.mysql.com/doc/index-other.html&https://dev.mysql.com/doc/employee/en/sakila-structure.html DQL:数据查询语言 https://dev.mysql.com/doc/refman/8.3/en/select.html 单表查询 --常用格式SELECTselection_list/*要查询的列名称*/FROMtable_list/*要查询的...
Statement).%New() s qStatus = tStatement.%Prepare(myquery) if qStatus '= 1 { w "%Prepare failed:" d $System.Status.DisplayError(qStatus) q } s rset = tStatement.%Execute(list) d rset.%Display() } FOR SOME %ELEMENT谓词可以包含逻辑操作符,也可以使用逻辑操作符链接到其他谓词。 下面...