11.7 SQL: in, between, like, and is null Operators

This section examines four special operators (other than the comparators =, <, etc.) that SQL provides for use within search conditions: in; ... between... and...; like; and is null . These are sometimes called "functions", and the conditions they are used to express are called "predicates" in the SQL standard.

A function is something that takes zero or more values as arguments and returns a single value as its result. You are probably familiar with functions from mathematics or programming, such as cos( x) or sqrt( x). As these examples illustrate, syntactically a function is usually represented as a function identifier preceding its arguments, which are typically included in parentheses.

When the action performed by a function is represented without bracketing all the arguments, we usually describe the notation as involving operators and operands rather than functions and arguments. Operators may be represented in infix, prefix, postfix, and mixfix notation according to whether the operator appears between, before, after, or mixed among the operands. For instance, in mathematics the sum of 2 and 3 might be set out as

sum(2, 3)            -- function2 + 3                -- infix operator+ 2 3             ...