Predicates are truth-tests.

Predicates are truth-tests. If the predicate test is true, it returns a value. Each predicate is evaluated per row, so that when the predicate is part of an entire table SELECT statement, the statement can return multiple results.

Predicates consist of a set of parameters and arguments. For example, in the following WHERE clause:

WHERE name = 'Smith'
  • name = 'Smith' is the predicate

  • 'Smith' is an expression