2   具体内容

 2.1  使用范围

SQL Server（2008开始） ；Azure SQL数据库；Azure  SQL数据仓库；并行数据仓库

2.2  语法

 是SQL Server数据库引擎评估以获取单个数据值的符号和运算符的组合。简单表达式可以是单个常量，变量，列或标量函数。运算符可用于将两个或多个简单表达式连接到一个复杂的表达式中。

— Syntax for SQL Server and Azure SQL Database
{ constant | scalar_function | [ table_name. ] column | variable
| ( expression ) | ( scalar_subquery )
| { unary_operator } expression
| expression { binary_operator } expression
| ranking_windowed_function | aggregate_windowed_function
}
— Syntax for Azure SQL Data Warehouse and Parallel Data Warehouse
— Expression in a SELECT statement
<expression> ::=
{
constant
| scalar_function
| column
| variable
| ( expression )
| { unary_operator } expression
| expression { binary_operator } expression
}
[ COLLATE Windows_collation_name ]
— Scalar Expression in a DECLARE, SET, IF…ELSE, or WHILE statement
<scalar_expression> ::=
{
constant
| scalar_function
| variable
| ( expression )
| (scalar_subquery )
| { unary_operator } expression
| expression { binary_operator } expression
}
[ COLLATE { Windows_collation_name ]