pg_attribute — PostgreSQL system catalog

The PostgreSQL pg_attribute system catalog: full column reference (names, types, descriptions), catalog relationships and version support.

The Sev-1 Admin
The Sev-1 Admin  ·  4 min read

Summary

The catalog pg_attribute 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 indeed all objects that have pg_class entries.)

(Description quoted from the official PostgreSQL documentation.)

Columns

The pg_attribute system catalog exposes the following columns (names, types and descriptions are taken verbatim from the PostgreSQL documentation):

  • attrelid oid references pg_class.oid
    The table this column belongs to
  • attname name
    The column name
  • atttypid oid references pg_type.oid
    The data type of this column (zero for a dropped column)
  • 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 ctid, have (arbitrary) negative numbers.
  • atttypmod int4
    atttypmod 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 atttypmod.
  • attndims int2
    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’s an array”.)
  • attbyval bool
    A copy of pg_type.typbyval of this column’s type
  • attalign char
    A copy of pg_type.typalign 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.
  • attcompression char
    The current compression method of the column. Typically this is ‘\0’ to specify use of the current default setting (see default_toast_compression). Otherwise, ‘p’ selects pglz compression, while ‘l’ selects LZ4 compression. However, this field is ignored whenever attstorage does not allow compression.
  • attnotnull bool
    This column has a (possibly invalid) not-null constraint.
  • atthasdef bool
    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 expression. (Check attgenerated to determine whether this is a default or a generation expression.)
  • atthasmissing bool
    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, v = virtual. A stored generated column is physically stored like a normal column. A virtual generated column is physically stored as a null value, with the actual value being computed at run time.
  • attisdropped bool
    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 bool
    This column is defined locally in the relation. Note that a column can be locally defined and inherited simultaneously.
  • attinhcount int2
    The number of direct ancestors this column has. A column with a nonzero number of ancestors cannot be dropped nor renamed.
  • attcollation oid references pg_collation.oid
    The defined collation of the column, or zero if the column is not of a collatable data type
  • attstattarget int2
    attstattarget controls the level of detail of statistics accumulated for this column by ANALYZE. A zero value indicates that no statistics should be collected. A null value says to use the system default statistics target. The exact meaning of positive values is data type-dependent. For scalar data types, attstattarget is both the target number of “most common values” to collect, and the target number of histogram bins to create.
  • 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.

Related catalogs

This object references the following other system catalogs:

Version applicability

Present in PostgreSQL 17, 18, 19 (verified against each release’s documentation). This is a long-standing system object that also exists in earlier PostgreSQL releases.

Related & references

Reference: PostgreSQL documentation — pg_attribute.