System Columns

System columns in a database table are automatically created and maintained by the database system to store metadata related to the table. The system columns are as follows:

• oid: object identifier, which is the unique identifier of each table in a database.
• ctid: row identifier, which is the unique identifier of each row in a table.
• xmin: transaction identifier, indicating the minimum transaction ID for inserting a row in a table.
• xmax: transaction identifier, indicating the maximum transaction ID for deleting or updating a row in a table.
• cmin and cmax: command identifiers, indicating the command IDs for inserting and deleting a row, respectively.
• xc_node_id: node identifier, which is used to identify the physical node where the data is located.