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  •     QAD Glossary

  • Managing Database Sequences
    When a unique identifier is needed by a program, the system often uses a control field to store the last number used. The system also supports the use of a special schema element called a sequence.
    A sequence is a database element used to generate a stream of sequential values for assigning unique identifiers to records. Sequences allow fast, accurate numbering, and reduce the amount of time the system spends validating uniqueness.
    Note: Because the sequence is generated at the database level, records viewed from within a domain may appear to have gaps.
    Use Sequence Report (36.16.15) to display a list of sequences defined in the database. The sequence description indicates the database table and field that is updated by the sequence. For example, the description of sequence cmt_sq01 is cmt_det.cmt_indx.
    Sequences have the important advantage of speed and reducing the possibility of record locking and contention. However, each sequence is a separate database element, distinct from the table to which it applies. This means that sequences must be initialized correctly whenever you use Database Table Dump/Load.
    If sequences are not initialized correctly, Duplicate Unique Key errors may occur when users attempt to create transactions.
    If dumping and loading are done as part of installing a software upgrade, sequence initialization is automatically performed by the installation utilities. However, if you perform a dump/load to consolidate tables or increase database size, you must initialize sequences yourself. This is true also if you consolidate data from two different databases.
    Use Database Sequence Initialization (36.16.17) to reset sequences to the highest value plus 1 after loading data.This program works with both Progress and Oracle databases.
    Use Sequence Maintenance (36.16.13) to manually reset a sequence number to a specific value in a Progress database.
    Use Sequence Inquiry (36.16.14) or Sequence Report (36.16.15) to view sequence information.
    To guarantee database integrity, perform sequence maintenance:
    In single-user mode sessions only
    As a required part of your standard database maintenance
    Note: To avoid accidental update to sequence structures, use menu security to protect sequence maintenance functions.