Pseudo-types v15

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Data typeNativeAliasDescription
any✅Indicates that a function accepts any input data type.
anyelement✅Indicates that a function accepts any data type. For more information, see Polymorphic types in the PostgreSQL documentation.
anyarray✅Indicates that a function accepts any array data type. For more information, see Polymorphic types in the PostgreSQL documentation.
anynonarray✅Indicates that a function accepts any non-array data type. For more information, see Polymorphic types in the PostgreSQL documentation.
anyenum✅Indicates that a function accepts any enum data type. For more information, see Polymorphic types and Enumerated types in the PostgreSQL documentation.
anyrange✅Indicates that a function accepts any range data type. For more information, see Polymorphic types and Range types in the PostgreSQL documentation.
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.
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.
void✅Indicates that a function returns no value.
opaque✅An obsolete type name that formerly served all the above purposes.

Overview

The PostgreSQL type system contains a number of special-purpose entries that are collectively called pseudo-types. A pseudo-type can't 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 doesn't correspond to taking or returning a value of a specific SQL data type.

Functions coded in C (whether built-in or dynamically loaded) can be declared to accept or return any of these pseudo data types. It's up to the function author to ensure that the function behaves 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 the use of a pseudo-type as an argument type. They 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 anyelement, anyarray, anynonarray, anyenum, and anyrange.

The internal pseudo-type is used to declare functions that are meant to be called only 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 can't be called from SQL. To preserve the type safety of this restriction, it's important to follow this coding rule: don't create any function that's declared to return internal unless it has at least one internal argument.

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