## 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

Column Type Description
`oid` `oid` Row identifier
`adrelid` `oid` (references `pg_class`.`oid`) The table this column belongs to
`adnum` `int2` (references `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.