Pseudo-types-PolarDB(PolarDB)-阿里云帮助中心

Pseudo-types are special type identifiers in the PolarDB for Oracle type system. They can appear as function argument or return types to express behaviors that ordinary type declarations cannot capture.

Polymorphic pseudo-types

Polymorphic pseudo-types let a single function definition work across multiple data types. They come in two families with different type-matching rules:

Name	Family	Description
`anyelement`	Simple	Accepts any data type.
`anyarray`	Simple	Accepts any array data type.
`anynonarray`	Simple	Accepts any non-array data type.
`anyenum`	Simple	Accepts any enum data type.
`anyrange`	Simple	Accepts any range data type.
`anymultirange`	Simple	Accepts any multirange data type.
`anycompatible`	Common	Accepts any data type, with automatic promotion of multiple arguments to a common data type.
`anycompatiblearray`	Common	Accepts any array data type, with automatic promotion to a common data type.
`anycompatiblenonarray`	Common	Accepts any non-array data type, with automatic promotion to a common data type.
`anycompatiblerange`	Common	Accepts any range data type, with automatic promotion to a common data type.
`anycompatiblemultirange`	Common	Accepts any multirange data type, with automatic promotion to a common data type.

Other pseudo-types

Name	Description
`any`	Accepts any input data type.
`cstring`	Accepts or returns a null-terminated C string.
`internal`	Accepts or returns a server-internal data type. See Security restrictions on `internal` for details.
`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`.
`table_am_handler`	A table access method handler is declared to return `table_am_handler`.
`index_am_handler`	An index access method handler is declared to return `index_am_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 available to event triggers.
`void`	Indicates that a function returns no value.
`unknown`	Identifies a not-yet-resolved type, such as an undecorated string literal.

Usage notes

C functions

Functions written in C — whether built-in or dynamically loaded — can be declared to accept or return any pseudo-type. The function author is responsible for ensuring the function behaves safely when a pseudo-type is used as an argument type.

Procedural language functions

Functions written in procedural languages can use pseudo-types only as permitted by their implementation language. Currently, most procedural languages forbid pseudo-types as argument types and allow only void and record as return types (plus trigger or event_trigger when the function is used as a trigger or event trigger).

Security restrictions on `internal`

internal is reserved for functions meant to be called only by the database system, not directly from SQL. A function with at least one internal-type argument cannot be called from SQL.

To maintain type safety, never declare a function as returning internal unless it has at least one internal argument.