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| title: pg_attribute |
| --- |
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| 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` entries.) The term attribute is equivalent to column. |
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| <span class="tablecap">Table 1. pg\_catalog.pg\_attribute</span> |
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| | column | type | references | description | |
| |-----------------|----------|---------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| |
| | `attrelid` | oid | pg\_class.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 | |
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