Updated on 2025-09-22 GMT+08:00
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.
Parent topic: Basic Concepts
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