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
   
  
| Name | Type | References | Description | 
|---|---|---|---|
| 
        oid
        | 
        oid
        | Row identifier | |
| 
        adrelid
        | 
        oid
        | 
        
          | The table this column belongs to | 
| 
        adnum
        | 
        int2
        | 
        
          | 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. |