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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.
Table 1. pg_catalog.pg_attribute
| 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 |
