pg_attribute
   The catalog pg_attribute stores information about
   table columns.  There will be exactly one
   pg_attribute row for every column in every
   table in the database.  (There will also be attribute entries for
   indexes, and indeed all objects that have
   pg_class
   entries.)
  
The term attribute is equivalent to column and is used for historical reasons.
Table 52.7. pg_attribute Columns
| Column Type Description | 
|---|
| 
        The table this column belongs to | 
| 
        The column name | 
| 
        The data type of this column (zero for a dropped column) | 
| 
        
        | 
| 
        
       A copy of  | 
| 
        
       The number of the column.  Ordinary columns are numbered from 1
       up.  System columns, such as  | 
| 
        Number of dimensions, if the column is an array type; otherwise 0. (Presently, the number of dimensions of an array is not enforced, so any nonzero value effectively means “it's an array”.) | 
| 
        Always -1 in storage, but when loaded into a row descriptor in memory this might be updated to cache the offset of the attribute within the row | 
| 
        
        | 
| 
        
       A copy of  | 
| 
        
       A copy of  | 
| 
        
       Normally a copy of  | 
| 
        
       The current compression method of the column.  Typically this is
        | 
| 
        This represents a not-null constraint. | 
| 
        
       This column has a default expression or generation expression, in which
       case there will be a corresponding entry in the
        | 
| 
        
       This column has a value which is used where the column is entirely
       missing from the row, as happens when a column is added with a
       non-volatile  | 
| 
        
       If a zero byte ( | 
| 
        
       If a zero byte ( | 
| 
        This column has been dropped and is no longer valid. A dropped column is still physically present in the table, but is ignored by the parser and so cannot be accessed via SQL. | 
| 
        This column is defined locally in the relation. Note that a column can be locally defined and inherited simultaneously. | 
| 
        The number of direct ancestors this column has. A column with a nonzero number of ancestors cannot be dropped nor renamed. | 
| 
        The defined collation of the column, or zero if the column is not of a collatable data type | 
| 
        Column-level access privileges, if any have been granted specifically on this column | 
| 
        Attribute-level options, as “keyword=value” strings | 
| 
        Attribute-level foreign data wrapper options, as “keyword=value” strings | 
| 
        
       This column has a one element array containing the value used when the
       column is entirely missing from the row, as happens when the column is
       added with a non-volatile  | 
   In a dropped column's pg_attribute entry,
   atttypid is reset to zero, but
   attlen and the other fields copied from
   pg_type are still valid.  This arrangement is needed
   to cope with the situation where the dropped column's data type was
   later dropped, and so there is no pg_type row anymore.
   attlen and the other fields can be used
   to interpret the contents of a row of the table.