(B)0relation-clause =

  qq> context-var qqq> IN qqwqqqqqqqqqqqqqqqqqqqqqwqq> relation-name qq>
                            mqq> db-handle qq> . qj

    In the relation-clause, you must declare context variables for a
    record stream or a loop. A context variable is a temporary name
    that identifies the record stream to Oracle Rdb.

    Once you have associated a context variable with a relation, you
    use the context variable to refer to fields from that relation.
    In this way, Oracle Rdb always knows which field from which relation
    you are referring to.

    You must use a context variable in every data manipulation
    statement and in every data definition statement that uses an
    RSE.

    If you access several record streams at once, the context
    variable lets you distinguish between fields from different
    record streams, even if different fields have the same name.

    In all programs except RDBPRE, RDML, SQL$PRE, and SQL$MOD
    programs, context variables must be unique within a request.