System Catalogs Definitions - pg_attribute - 《Greenplum Database v6.23 Documentation》

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.

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`	int4		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`	int2		A copy of `pg_type.typlen` of this column’s type.
`attnum`	int2		The number of the column. Ordinary columns are numbered from 1 up. System columns, such as oid, have (arbitrary) negative numbers.
`attndims`	int4		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`	int4		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`	int4		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 activate or deactivate 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`	int4		The number of direct ancestors this column has. A column with a nonzero number of ancestors cannot be dropped nor renamed.
`attcollation`	oid	pg_collation.oid	The defined collation of the column, or zero if the is not of a collatable data type.
`attacl`	aclitem[]		Column-level access privileges, if any have been granted specifically on this column.
`attoptions`	text[]		Attribute-level options, as “keyword=value” strings.
`attfdwoptions`	text[]		Attribute-level foreign data wrapper options, as “keyword=value” strings.

Parent topic: System Catalogs Definitions