The DECLARE statement defines global and local variables for use
       as value expressions. When DEC DATATRIEVE initializes a variable,
       it assigns the variable the MISSING VALUE or DEFAULT VALUE if one
       is specified in the DECLARE statement. DEC DATATRIEVE assigns a
       value of zero to numeric variables and a space to alphabetic and
       alphanumeric variables if no MISSING VALUE or DEFAULT VALUE is
       specified.

1  –  Global Variables

       You can define global variables only with DECLARE statements
       entered in response to the DTR> prompt of DEC DATATRIEVE command
       level.

       You can use a global variable as a value expression in any DEC
       DATATRIEVE statement. Unless you define a global variable with
       a COMPUTED BY clause, the global variable retains the value you
       assign to it until you either assign it a new value or release it
       with the RELEASE command.

       The value of a global variable defined with a COMPUTED BY clause
       depends on the value expression that controls the computation.
       For example, you can declare the value of the variable to be 1.2
       times the price of a boat in the YACHTS domain. The value of the
       variable changes according to the value of the PRICE field for
       different records:

       DTR> READY YACHTS
       DTR> DECLARE VAR COMPUTED BY PRICE * 1.2.
       DTR> FOR FIRST 5 YACHTS PRINT VAR USING $$$,$$$.99

          VAR

       $44,341.20
       $21,480.00
       $33,000.00
       $22,320.00
       $11,874.00

       DTR>

2  –  Local Variables

       You can define local variables with DECLARE statements entered in
       BEGIN-END and THEN statements.

       A local variable is released as soon as DEC DATATRIEVE completes
       the execution of the clause or statement in which it was
       declared. Although a local variable stays in effect for
       subsequent statements of the compound statement in which it is
       declared, it has no meaning in any outer statements containing
       that compound statement.

3  –  Null Values and Variables

       DEC DATATRIEVE supports relational databases null values in
       variables. Therefore, DEC DATATRIEVE has the following behavior:

       o  When transferring a missing value from a DEC DATATRIEVE
          variable to a relational field, the field receives a null
          value.

          DTR> DECLARE VAR PIC X(10) MISSING VALUE "77".
          DTR> PRINT VAR

          VAR

          77

          DTR> STORE EMPLOYEE_MANAGER_TABLE USING EMP_ID = VAR
          DTR> PRINT EMPLOYEE_MANAGER_TABLE

           EMP_ID          MGR_ID

              NULL        NULL
          DTR>

       o  When transferring a null value from a relational field to a
          DEC DATATRIEVE variable, the variable receives either its
          missing value (if a MISSING VALUE clause is specified in the
          variable definition), or a null value (if the variable does
          not contain a MISSING VALUE clause).

          DTR> DECLARE EMPLOYEE PIC X(10) MISSING VALUE 8999.
          DTR> FOR X IN EMPLOYEE_MANAGER_TABLE
          CON> EMPLOYEE = EMP_ID
          DTR> PRINT EMPLOYEE

           EMPLOYEE

          8999
          DTR> DECLARE MANAGER PIC X(10).
          DTR> FOR X IN EMPLOYEE_MANAGER_TABLE
          CON> MANAGER = MGR_ID
          DTR> PRINT MANAGER

           MANAGER

          NULL
          DTR>