Predicate

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A predicate is the syntax used to specify a subset of rows to be returned. Predicates are specified in the WHERE clause of a SQL statement.

In the example below "EMPNO=7788" is a predicate:

SELECT * FROM emp
 WHERE empno = 7788;

The predicate in this example will evaluate to:

  • true, if the empno column has a value of 7788;
  • false, if the empno contains any other value (not '7788'); or
  • unknown, if the empno column is NULL.

More complicated predicates can contain operators like:

  • >, <, >=, <=, <> or !=
  • IS NULL/ IS NOT NULL
  • LIKE
  • BETWEEN
  • AND, OR, NOT
  • Etc.
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