The catalog pg_authid contains information about database authorization identifiers (roles). A role subsumes the concepts of "users" and "groups". A user is essentially just a role with the rolcanlogin flag set. Any role (with or without rolcanlogin) can have other roles as members; see pg_auth_members. Since this catalog contains passwords, it must not be publicly readable. pg_roles is a publicly readable view on pg_authid that blanks out the password field. Chapter 21 contains detailed inform

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.) The term attribute is equivalent to column and is used for historical reasons. Table 50-7. pg_attribute Columns Name Type References Description attrelid oid pg_class.oid The table this column belongs to attname name The column name at

The catalog pg_attrdef stores column default values. The main information about columns is stored in pg_attribute (see below). Only columns that explicitly specify a default value (when the table is created or the column is added) will have an entry here. Table 50-6. pg_attrdef Columns Name Type References Description oid oid Row identifier (hidden attribute; must be explicitly selected) adrelid oid pg_class.oid The table this column belongs to adnum int2 pg_attribute.attnum The number of t

The catalog pg_amproc stores information about support procedures associated with access method operator families. There is one row for each support procedure belonging to an operator family. Table 50-5. pg_amproc Columns Name Type References Description oid oid Row identifier (hidden attribute; must be explicitly selected) amprocfamily oid pg_opfamily.oid The operator family this entry is for amproclefttype oid pg_type.oid Left-hand input data type of associated operator amprocrighttype oi

The catalog pg_amop stores information about operators associated with access method operator families. There is one row for each operator that is a member of an operator family. A family member can be either a search operator or an ordering operator. An operator can appear in more than one family, but cannot appear in more than one search position nor more than one ordering position within a family. (It is allowed, though unlikely, for an operator to be used for both search and ordering purpos

The catalog pg_am stores information about relation access methods. There is one row for each access method supported by the system. Currently, only indexes have access methods. The requirements for index access methods are discussed in detail in Chapter 59. Table 50-3. pg_am Columns Name Type References Description oid oid Row identifier (hidden attribute; must be explicitly selected) amname name Name of the access method amhandler oid pg_proc.oid OID of a handler function that is respon

The catalog pg_aggregate stores information about aggregate functions. An aggregate function is a function that operates on a set of values (typically one column from each row that matches a query condition) and returns a single value computed from all these values. Typical aggregate functions are sum, count, and max. Each entry in pg_aggregate is an extension of an entry in pg_proc. The pg_proc entry carries the aggregate's name, input and output data types, and other information that is simil

PostgreSQL allows functions that have named parameters to be called using either positional or named notation. Named notation is especially useful for functions that have a large number of parameters, since it makes the associations between parameters and actual arguments more explicit and reliable. In positional notation, a function call is written with its argument values in the same order as they are defined in the function declaration. In named notation, the arguments are matched to the fun

btree_gist provides GiST index operator classes that implement B-tree equivalent behavior for the data types int2, int4, int8, float4, float8, numeric, timestamp with time zone, timestamp without time zone, time with time zone, time without time zone, date, interval, oid, money, char, varchar, text, bytea, bit, varbit, macaddr, inet, and cidr. In general, these operator classes will not outperform the equivalent standard B-tree index methods, and they lack one major feature of the standard B-tr

btree_gin provides sample GIN operator classes that implement B-tree equivalent behavior for the data types int2, int4, int8, float4, float8, timestamp with time zone, timestamp without time zone, time with time zone, time without time zone, date, interval, oid, money, "char", varchar, text, bytea, bit, varbit, macaddr, inet, and cidr. In general, these operator classes will not outperform the equivalent standard B-tree index methods, and they lack one major feature of the standard B-tree code: