Specifies a predicate that SQL evaluates to generate an
    intermediate result table. SQL evaluates the predicate for each
    row of the intermediate result table created by the FROM clause.
    The rows of that table for which the predicate is true become
    another intermediate result table for later clauses in a select
    expression.

    Column names specified in the predicate of the WHERE clause must
    either:

    o  Identify columns of the intermediate result table created by
       the FROM clause.

    o  Be an outer reference (possible only if the WHERE clause is
       part of a column select expression). See Outer_References for
       more information on outer references.

    In general, the predicate in a WHERE clause cannot refer to an
    aggregate function. For instance, the following statement is
    invalid:

    SQL> SELECT * FROM EMPLOYEES WHERE MAX(LAST_NAME) > 'X';
    %SQL-F-INVFUNREF, Invalid function reference