Using the WITH VERCOLS Option

Use the WITH VERCOLS keywords to create two shadow columns that HCL OneDB™ uses to support update operations on secondary servers.

The first column, ifx_insert_checksum, contains a checksum of the row when it was first created. The second column, ifx_row_version, contains a version number of the row. When a row is first inserted, ifx_insert_checksum is generated, and ifx_row_version will be set to one. Each time the row is updated, ifx_row_version is incremented by one, but ifx_insert_checksum does not change. These two columns are visible shadow columns because they can be indexed and can be viewed in system catalog tables.

For most database operations, the ifx_insert_checksum and ifx_row_version columns are hidden. For example, if you include the WITH VERCOLS keywords when you create a table, the ifx_insert_checksum and ifx_row_version columns have the following behavior:

They are not returned by queries that specify an asterisk ( * ) as the projection list, as in the statement:
```
SELECT * FROM tablename;
```
They appear in DB-Access when you ask for information about the columns of the table.
They are included in the number of columns (ncols) in the systables system catalog table entry for tablename.

To view the contents of ifx_insert_checksum and ifx_row_version, you must explicitly specify the column names in the projection list of a SELECT statement, as the following example shows:

SELECT ifx_insert_checksum, ifx_row_version FROM tablename;

When row versioning is enabled, ifx_row_version is incremented by one each time the row is updated; however, row updates made by Enterprise Replication do not increment the row version. To update the row version on a server using Enterprise Replication, you must include the ifx_row_version column in the replicate participant definition.

For more information about how to use this option, refer to the HCL OneDB Administrator's Guide.