Drop Down MenusCSS Drop Down MenuPure CSS Dropdown Menu

Postgresql Pseudo Data Types

  • The PostgreSQL type system contains a number of special-purpose entries that are collectively called pseudo-types. 
  • A pseudo-type cannot be used as a column data type, but it can be used to declare a function's argument or result type. Each of the available pseudo-types is useful in situations where a function's behavior does not correspond to simply taking or returning a value of a specific SQL data type
Name
Description
any
Indicates that a function accepts any input data type.
anyelement
Indicates that a function accepts any data type
anyarray
Indicates that a function accepts any array data type
anynonarray
Indicates that a function accepts any non-array data type
anyenum
Indicates that a function accepts any enum data type
anyrange
Indicates that a function accepts any range data type
cstring
Indicates that a function accepts or returns a null-terminated C string.
internal
Indicates that a function accepts or returns a server-internal data type.
language_handler
A procedural language call handler is declared to return language_handler.
fdw_handler
A foreign-data wrapper handler is declared to return fdw_handler.
tsm_handler
A tablesample method handler is declared to return tsm_handler.
record
Identifies a function taking or returning an unspecified row type.
trigger
A trigger function is declared to return trigger.
event_trigger
An event trigger function is declared to return event_trigger.
pg_ddl_command
Identifies a representation of DDL commands that is available to event triggers.
void
Indicates that a function returns no value.
opaque
An obsolete type name that formerly served all the above purposes.
  • Functions coded in C (whether built-in or dynamically loaded) can be declared to accept or return any of these pseudo data types. It is up to the function author to ensure that the function will behave safely when a pseudo-type is used as an argument type.
  • Functions coded in procedural languages can use pseudo-types only as allowed by their implementation languages. At present most procedural languages forbid use of a pseudo-type as an argument type, and allow only void and record as a result type (plus trigger or event_trigger when the function is used as a trigger or event trigger). Some also support polymorphic functions using the types anyelementanyarrayanynonarrayanyenum, and anyrange.
  • The internal pseudo-type is used to declare functions that are meant only to be called internally by the database system, and not by direct invocation in an SQL query. If a function has at least one internal-type argument then it cannot be called from SQL. To preserve the type safety of this restriction it is important to follow this coding rule: do not create any function that is declared to return internal unless it has at least one internal argument.

Comments

Popular posts from this blog

PostgreSQL Pgbadger Installation On Linux

PostgreSQL pgBadger

How to configure Replication Manager (repmgr) ?

Migrating From Oracle to PostgreSQL using ora2pg open source tools

How To Schedule PostgreSQL Jobs using pgAgent on Linux plateform