A value expression is a symbol or string of symbols that you
    use to calculate a value. When you use a value expression in
    a statement, Oracle Rdb calculates the value associated with the
    expression and uses it when executing the statement.

    The RDML value expressions are:

    o  Arithmetic

    o  Database Field Value

    o  FIRST FROM

    o  Host Variable

    o  RDB$DB_KEY

    o  RDB$MISSING

    For more information and the syntax diagrams see the HELP entries
    for each of these expressions.

1  –  Format

  (B)0value-expr =

    qqqwqqq> host-variable qqqqqqqqqqqqwqqq>
       tqqq> db-field qqqqqqqqqqqqqqqqqu
       tqqq> quoted-string qqqqqqqqqqqqu
       tqqq> numeric-literal qqqqqqqqqqu
       tqqq> statistical-expr qqqqqqqqqu
       tqqq> arithmetic-expr qqqqqqqqqqu
       tqqq> missing-value qqqqqqqqqqqqu
       tqqq> first-expr  qqqqqqqqqqqqqqu
       tqqq> concat-expr qqqqqqqqqqqqqqu
       tqqq> dbkey  qqqqqqqqqqqqqqqqqqqu
       tqqq> ( qq> value-expr qq> ) qqqu
       tqqq> -  qq> value-expr qqqqqqqqu
       mqqq> +  qq> value-expr qqqqqqqqj

    The concat-expr consists of the concatenate operator ( | ) and
    two value expressions. The concat-expr joins the second value
    expression to the first value expression.