Expressions
Expressions are composed of various operators and operands that evaluate to either a single value or a set of values. Some expressions do not use operators. For example, a column name is an expression. Constants are expressions also. Expressions are used in many contexts, such as specifying values to be retrieved (in a select clause) or compared (in a where clause). For example:
select empname, empage from employee
where salary <String `75000'> >
In this example, empname and empage are expressions representing the column values to be retrieved, salary is an expression representing a column value to be compared, and 75000 is an integer literal expression.
An expression can be enclosed in parentheses, such as ('J. J. Jones'), without affecting its meaning.