An expression is a series of operands and operators that you specify when you write a program or function script.
Each expression resolves to a particular type of value at run time. A numeric expression resolves to a number; a string expression resolves to a series of characters; a logical expression resolves to true or false; a datetime expression resolves to a date, interval, time, or timestamp.
Expressions are evaluated in accordance with a set of precedence rules and (within a given level of precedence) from left to right, but you can use parentheses to force a different ordering. A nested parenthetical subexpression is evaluated before the enclosing parenthetical subexpression, and all parenthetical expressions are evaluated before the expression as a whole.
"A value = " + 1 + 2
"A value = 12"
"A value = " + (1 + 2)
"A value = 3"
Related reference
Datetime expressions
Logical expressions
Numeric expressions
Text expressions