An expression is a combination of one or more constants, literals, functions, column identifiers, and variables, separated by operators, that returns a single value. Expressions can be of several types, including arithmetic, relational, logical (or Boolean), and character string. In some Transact-SQL clauses, a subquery can be used in an expression. A case expression can be used in an expression.
Use parentheses to group the elements in an expression. When “expression” is given as a variable in a syntax statement, a simple expression is assumed. “Logical expression” is specified when only a logical expression is acceptable.
