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 53.6. pg_attrdef Columns
Column Type Description  | 
|---|
        Row identifier  | 
        The table this column belongs to  | 
        The number of the column  | 
        
       The column default value, in   |