Specifies a search condition that controls how many times SQL can
    execute a compound statement.

    SQL evaluates the WHILE search condition. If it evaluates to
    TRUE, SQL executes the associated sequence of SQL statements. If
    SQL does not encounter an error exception, control returns to the
    WHILE clause at the top of the loop for subsequent evaluation.
    Each time the search condition evaluates to TRUE, the WHILE-
    DO statement executes the SQL statements embedded within its
    DO . . . END WHILE block. If the search condition evaluates to
    FALSE or UNKNOWN, SQL bypasses the DO . . . END WHILE block and
    passes control to the next statement.