---
title: "pg_attrdef"
id: catalog-pg-attrdef
pg_version: "20devel"
---

<a id="catalog-pg-attrdef"></a>

## 52.6. pg_attrdef

The catalog pg_attrdef stores column default expressions and generation expressions. The main information about columns is stored in [pg_attribute](catalog-pg-attribute.md). Only columns for which a default expression or generation expression has been explicitly set will have an entry here. 

**pg_attrdef Columns**

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