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 entries.) The term attribute is equivalent to column.

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 address 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

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 ctid, have
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.
atthasdef	boolean		This column has a default expression or generation expression, in which case there will be a corresponding entry in the pg_attrdef catalog that actually defines the value. (Check attgenerated to determine whether this is a default or a generation expression.)
atthasmissing	boolean		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 DEFAULT value after the row is created. The actual value used is stored in the attmissingval column.
attidentity	char		If a zero byte (‘’), then not an identity column. Otherwise, a = generated always, d = generated by default.
attgenerated	char		If a zero byte (‘’), then not a generated column. Otherwise, s = stored. (Other values might be added in the future.)
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.
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.
attmissingval	anyarray		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 DEFAULT value after the row is created. The value is only used when atthasmissing is true. If there is no value the column is null.