# pg_attribute

The `pg_attribute` table 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 all objects that have `pg_class_internal` entries.) The term attribute is equivalent to column.



Table 1. `pg_catalog.pg_attribute`

| column          | type     | references            | description                                                  |
| :-------------- | :------- | :-------------------- | :----------------------------------------------------------- |
| `attrelid`      | oid      | pg_class_internal.oid | The table this column belongs to                             |
| `attname`       | name     |                       | The column name                                              |
| `atttypid`      | oid      | pg_type.oid           | The data type of this column                                 |
| `attstattarget` | integer  |                       | Controls the level of detail of statistics accumulated for this column by `ANALYZE`. A zero value indicates that no statistics should be collected. A negative value says to use the system default statistics target. The exact meaning of positive values is data type-dependent. For scalar data types, it is both the target number of “most common values” to collect, and the target number of histogram bins to create. |
| `attlen`        | smallint |                       | A copy of pg_type.typlen of this column’s type.              |
| `attnum`        | smallint |                       | The number of the column. Ordinary columns are numbered from 1 up. System columns, such as oid, have (arbitrary) negative numbers. |
| `attndims`      | integer  |                       | 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 is an array) |
| `attcacheoff`   | integer  |                       | Always `-1` in storage, but when loaded into a row descriptor in memory this may be updated to cache the offset of the attribute within the row |
| `atttypmod`     | integer  |                       | Records type-specific data supplied at table creation time (for example, the maximum length of a varchar column). It is passed to type-specific input functions and length coercion functions. The value will generally be `-1` for types that do not need it. |
| `attbyval`      | boolean  |                       | A copy of pg_type.typbyval of this column’s type             |
| `attstorage`    | char     |                       | Normally a copy of `pg_type.typstorage` of this column’s type. For TOAST-able data types, this can be altered after column creation to control storage policy. |
| `attalign`      | char     |                       | A copy of `pg_type.typalign` of this column’s type           |
| `attnotnull`    | boolean  |                       | This represents a not-null constraint. It is possible to change this column to enable or disable the constraint. |
| `atthasdef`     | boolean  |                       | This column has a default value, in which case there will be a corresponding entry in the `pg_attrdef` catalog that actually defines the value |
| `attisdropped`  | boolean  |                       | 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 |
| `attislocal`    | boolean  |                       | This column is defined locally in the relation. Note that a column may be locally defined and inherited simultaneously |
| `attinhcount`   | integer  |                       | The number of direct ancestors this column has. A column with a nonzero number of ancestors cannot be dropped nor renamed |