Before Progress Version 7, the only way ABL could generate sequential values was to maintain integer fields in a table record created specifically for this purpose. This is often done in a control table, separate from all other application tables.

For example, you might have a control table named syscontrol that contains the field last–cus–num. This field holds the value of the CustNum field for the last Customer record. The following code fragment generates a new Customer record with a unique Customer number:

. . .
DEFINE VARIABLE next-custnum NO-UNDO LIKE Customer.CustNum.

DO FOR syscontrol:
  DO TRANSACTION:
    FIND FIRST syscontrol EXCLUSIVE-LOCK.
    next-custnum = syscontrol.last-cus-num + 1.
    syscontrol.last-cus-num = next-custnum.
  END. /* transaction */
  RELEASE syscontrol.
END.

DO TRANSACTION:
  CREATE Customer.
  Customer.CustNum = next-custnum.
  DISPLAY Customer.
  UPDATE Customer.
END. /* transaction */
. . .

Note that access to the syscontrol table must be made within a small transaction to avoid lock contention problems.

Sequences provide a built-in means for generating incremental values, but they are not suitable for all applications. In certain situations (described in the following sections), you might need to use a control table, instead.

The following table compares sequences and control tables.