48.6. pg_attrdef
The catalog pg_attrdef stores column default values. The main information about columns is stored in pg_attribute (see below). Only columns that explicitly specify a default value (when the table is created or the column is added) will have an entry here.
Table 48-6. pg_attrdef Columns
| Name | Type | References | Description |
|---|---|---|---|
| oid | oid | Row identifier (hidden attribute; must be explicitly selected) | |
| 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 internal representation of the column default value | |
| adsrc | text | A human-readable representation of the default value |
The adsrc field is historical,
and is best not used, because it does not track outside changes
that might affect the representation of the default value.
Reverse-compiling the adbin field
(with pg_get_expr for example) is a
better way to display the default value.