ROWID columns

Informix®

When creating a table, Informix automatically adds a ROWID integer column (applies to non-fragmented tables only).

The ROWID column is auto-filled with a unique number and can be used like a primary key to access a given row.

Note:

Informix ROWID usage was a common practice in the early days of Informix 4GL programming. Today it is recommended to define all your database tables with a PRIMARY KEY to uniquely identify rows.

With Informix, the sqlca.sqlerrd[6] register contains the ROWID of the last row affected by an INSERT, UPDATE or DELETE statement.

PostgreSQL

Until PostgreSQL version 11, the OID system columns can be enabled when setting the default_with_oids server configuration parameter. OID columns are unsigned integers that can be used as unique row identifier. Starting with PostgreSQL version 12, OID columns are no longer supported. The type of PostgreSQL OID columns is INTEGER. The PostgreSQL C API provides the PQoidValue() function, to get the OID of the last inserted row. Unlike Informix sqlca.sqlerrd[6], PostgreSQL does not return the OID of the last row modified by an UPDATE, or removed by a DELETE. Starting with PostgreSQL version 12, OID system columns are no longer supported by PostgreSQL.

PostgreSQL tables have a CTID system column, but the value of this column defines the storage location of the row, the value changes when updating.

Solution

The PostgreSQL database driver automatically converts ROWID keywords to OID, assuming that the PostgreSQL version supports user-table OIDs.

Starting with PostgreSQL 12, user-table OIDs are no longer supported, and therefore, ROWID columns can no longer be emulated.

As a general SQL programming pattern, get rid of ROWID usage and use PRIMARY KEY columns to identify database table rows.

For databases where the keyword of the rowid pseudo-column is different than "ROWID", the translation can be controlled with the following FGLPROFILE entry:
dbi.database.dsname.ifxemul.rowid = { true | false }
For more details see IBM Informix emulation parameters in FGLPROFILE.