PRODUCT :  R:BASE                  VERSION    :  3.1 AND UP
     (From Ken Everett, Sequitur Systems, 117 Wallace Drive, Tullahoma,
     TN 37388. You can reach him at (615) 454-9017. Ken is a R:BASE
     instructor and application developer.)
     When you use the CREATE VIEW command, the column list and WHERE
     conditions in the SELECT clause can reference both system and global
     variables. The data the resulting view displays can vary depending on
     placement of parentheses around variables within the command. Examples
     in this article are based on the sample CONCOMP database shipped with
     Column Expressions
     Columns in a view can be defined as the result of an expression in the
     SELECT clause. For example, the following command creates a view with
     a column (days) that contains the number of days between the transaction
     date column and a date variable:
     SET VAR vdate DATE = 10/15/91
     CREATE VIEW since (transid, days) AS SELECT transid, +
      (.vdate - transdate) FROM transmaster
     This view could be used as the basis of an aging report, as was shown
     by Bill Downall in the July/August 1991 issue of the R:BASE Exchange.
     The first several records look like this when selected:
     transid             days
     -------             ----
        4760             1015
        4780             1009
        4790             1008
        4795             1006
        4800              964
     The parentheses around the date expression (.vdate - transdate) are not
     required for the CREATE VIEW command to work, but if you leave the
     parentheses out the results can be different.
     When the expression is enclosed in parentheses, the variable reference
     is stored as part of the view definition. If the parentheses are left
     out, the current variable value is stored with the view definition.
     Thus, with parentheses included in the example above, the values
     displayed by the view for the column days are dependent on the current
     value of the variable vdate. Without parentheses in the example above,
     the values from the view for the column days are always relative to
     WHERE Conditions
     Variable references used in WHERE clauses of views operate the same
     way with respect to parentheses. For example, to create a view of
     transactions for the customer whose ID number is in the variable
     vcustid, use either of the following:
     SET VAR vcustid INT = 101
     CREATE VIEW Cust1Trans AS SEL * FROM transmaster +
      WHERE custid = .vcustid
     SET VAR vcustid INT = 101
     CREATE VIEW Cust2Trans AS SEL * FROM transmaster +
      WHERE custid = (.vcustid)
     A view based on the first CREATE VIEW command shows transactions for
     customer 101 regardless of the current value of vcustid. In fact, the
     variable vcustid does not need to exist to use the view Cust1Trans. A
     view based on the second CREATE VIEW command cannot, however, be used
     unless the variable vcustid exists and has a proper data type and value.
     The second view definition gives different results as the value of
     vcustid changes.
     The SYSVIEWS System Table
     When you use the CREATE VIEW command, R:BASE stores the view definition
     in a system table called SYSVIEWS. You can look at the way R:BASE saves
     your views by browsing or editing the contents of the SYSVIEWS table
     with the BROWSE or EDIT commands. Be cautious about changing any of the
     column values when you do this.
     When you use variable references in the SELECT clause of a CREATE VIEW
     command, remember that the use of parentheses can affect the resulting
     view. If a variable reference is enclosed in parentheses, the variable
     name is stored in the actual view definition. If not, the value of the
     variable at the time the view was created is stored in the view