Transact-SQL语言使用的流程控制命令与常见的程序语言类似主要有以下几种控制命令。 4.6.1IF…ELSE其语法如下: IF<条件表达式> <命令行或程序块> [ELSE[条件表达式] <命令行或程序块>] 其中<条件表达式>可以是各种表达式的组合,但表达式的值必须是逻辑值“真”或“假”。ELSE子句是可选的,最简单的IF语句没有EL...
BEGIN…END用来设定一个语句块,可以将多条Transact-SQL语句封装起来构成一个语句块,在处理时,整个语句块被视为一条语句。BEGIN…END经常用在条件语句中,如IF…ELSE 或WHILE循环中。BEGIN…END语句可以嵌套使用。 2.判断语句(IF…ELSE) 通常计算机是按顺序执行程序中的语句,但是在许多情况下,语句执行的顺序以及是否...
select@@lock_timeout;--返回当前会话的当前锁定超时设置(毫秒) select@@max_connections;--返回SQL Server 实例允许同时进行的最大用户连接数 select@@MAX_PRECISIONAS'Max Precision';--返回decimal 和numeric 数据类型所用的精度级别 select@@SERVERNAME;--SQLServer 的本地服务器的名称 select@@SERVICENAME;--...
Transact-SQL 語法慣例 語法 syntaxsql IFboolean_expression{sql_statement|statement_block} [ELSE{sql_statement|statement_block} ] 引數 boolean_expression 傳回 或FALSE的TRUE表達式。 如果布爾表達式包含SELECT語句,SELECT語句必須以括弧括住。 {sql_statement|statement_block} ...
else if @y > @z print 'y > z' else print 'z > y' 9、CASE语句 use pangu update employee set e_wage = case when job_level = ’1’then e_wage*1.08 when job_level = ’2’then e_wage*1.07 when job_level = ’3’then e_wage*1.06 ...
Transact-SQL 語法慣例 語法 syntaxsql IFboolean_expression{sql_statement|statement_block} [ELSE{sql_statement|statement_block} ] 引數 boolean_expression 傳回 或FALSE的TRUE表達式。如果boolean_expression包含SELECT語句,SELECT語句必須以括弧括住。 使用語句區塊所定義的任何有效 Transact-SQL 語句或語句群組。 若...
Imposes conditions on the execution of a Transact-SQL statement. The Transact-SQL statement (sql_statement) following the boolean_expression is executed if the boolean_expression evaluates to TRUE. The optional ELSE keyword is an alternate Transact-SQL statement that is executed when boolean_...
Any Transact-SQL statement or statement grouping as defined by using a statement block. Unless a statement block is used, the IF or ELSE condition can affect the performance of only one Transact-SQL statement.To define a statement block, use the control-of-flow keywords BEGIN and END....
Imposes conditions on the execution of a Transact-SQL statement. The Transact-SQL statement (sql_statement) following the boolean_expression is executed if the boolean_expression evaluates to TRUE. The optional ELSE keyword is an alternate Transact-SQL statement that is executed when boolean_expression...
Imposes conditions on the execution of a Transact-SQL statement. The Transact-SQL statement (sql_statement) following the boolean_expression is executed if the boolean_expression evaluates to TRUE. The optional ELSE keyword is an alternate Transact-SQL statement that is executed when boolean_expression...