52.6. 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 52.6. 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.
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https://www.postgresql.org/docs/11/catalog-pg-attrdef.html