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attisdropped boolean   This column has been dropped and is no longer valid.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

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