## 51.6. `pg_attrdef`

The catalog `pg_attrdef` stores column default values. The main information about columns is stored in `pg_attribute`. Only columns for which a default value has been explicitly set will have an entry here.

Table 51.6. `pg_attrdef` Columns

Name | Type | References | Description
--- | --- | --- | ---
`oid` | `oid` |  | Row identifier
`adrelid` | `oid` | ``pg_class`.oid` | The table this column belongs to
`adnum` | `int2` | ``pg_attribute`.attnum` | The number of the column
`adbin` | `pg_node_tree` |  | The column default value, in `nodeToString()` representation. Use `pg_get_expr(adbin, adrelid)` to convert it to an SQL expression.