## 52.6. `pg_attrdef`

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 The catalog `pg_attrdef` stores column default values. The main information about columns is stored in [`pg_attribute`](catalog-pg-attribute.html). Only columns for which a default value has been explicitly set will have an entry here.

**Table 52.6. `pg_attrdef` Columns**

|                                                                  Column Type<br/><br/> Description                                                                 |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------|
|                                                                `oid` `oid`<br/><br/> Row identifier                                                                |
|                         `adrelid` `oid` (references [`pg_class`](catalog-pg-class.html).`oid`)<br/><br/> The table this column belongs to                          |
|                        `adnum` `int2` (references [`pg_attribute`](catalog-pg-attribute.html).`attnum`)<br/><br/> The number of the column                         |
|`adbin` `pg_node_tree`<br/><br/> The column default value, in `nodeToString()` representation. Use `pg_get_expr(adbin, adrelid)` to convert it to an SQL expression.|

