<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <HTML ><HEAD ><TITLE >Pseudo-Types</TITLE ><META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK REV="MADE" HREF="mailto:pgsql-docs@postgresql.org"><LINK REL="HOME" TITLE="PostgreSQL 9.6.4 Documentation" HREF="index.html"><LINK REL="UP" TITLE="Data Types" HREF="datatype.html"><LINK REL="PREVIOUS" TITLE="pg_lsn Type" HREF="datatype-pg-lsn.html"><LINK REL="NEXT" TITLE="Functions and Operators" HREF="functions.html"><LINK REL="STYLESHEET" TYPE="text/css" HREF="stylesheet.css"><META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=ISO-8859-1"><META NAME="creation" CONTENT="2017-08-11T02:27:18"></HEAD ><BODY CLASS="SECT1" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="4" ALIGN="center" VALIGN="bottom" ><A HREF="index.html" >PostgreSQL 9.6.4 Documentation</A ></TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A TITLE="pg_lsn Type" HREF="datatype-pg-lsn.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A HREF="datatype.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="60%" ALIGN="center" VALIGN="bottom" >Chapter 8. Data Types</TD ><TD WIDTH="20%" ALIGN="right" VALIGN="top" ><A TITLE="Functions and Operators" HREF="functions.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="SECT1" ><H1 CLASS="SECT1" ><A NAME="DATATYPE-PSEUDO" >8.20. Pseudo-Types</A ></H1 ><P > The <SPAN CLASS="PRODUCTNAME" >PostgreSQL</SPAN > type system contains a number of special-purpose entries that are collectively called <I CLASS="FIRSTTERM" >pseudo-types</I >. 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 <ACRONYM CLASS="ACRONYM" >SQL</ACRONYM > data type. <A HREF="datatype-pseudo.html#DATATYPE-PSEUDOTYPES-TABLE" >Table 8-25</A > lists the existing pseudo-types. </P ><DIV CLASS="TABLE" ><A NAME="DATATYPE-PSEUDOTYPES-TABLE" ></A ><P ><B >Table 8-25. Pseudo-Types</B ></P ><TABLE BORDER="1" CLASS="CALSTABLE" ><COL><COL><THEAD ><TR ><TH >Name</TH ><TH >Description</TH ></TR ></THEAD ><TBODY ><TR ><TD ><TT CLASS="TYPE" >any</TT ></TD ><TD >Indicates that a function accepts any input data type.</TD ></TR ><TR ><TD ><TT CLASS="TYPE" >anyelement</TT ></TD ><TD >Indicates that a function accepts any data type (see <A HREF="extend-type-system.html#EXTEND-TYPES-POLYMORPHIC" >Section 36.2.5</A >).</TD ></TR ><TR ><TD ><TT CLASS="TYPE" >anyarray</TT ></TD ><TD >Indicates that a function accepts any array data type (see <A HREF="extend-type-system.html#EXTEND-TYPES-POLYMORPHIC" >Section 36.2.5</A >).</TD ></TR ><TR ><TD ><TT CLASS="TYPE" >anynonarray</TT ></TD ><TD >Indicates that a function accepts any non-array data type (see <A HREF="extend-type-system.html#EXTEND-TYPES-POLYMORPHIC" >Section 36.2.5</A >).</TD ></TR ><TR ><TD ><TT CLASS="TYPE" >anyenum</TT ></TD ><TD >Indicates that a function accepts any enum data type (see <A HREF="extend-type-system.html#EXTEND-TYPES-POLYMORPHIC" >Section 36.2.5</A > and <A HREF="datatype-enum.html" >Section 8.7</A >).</TD ></TR ><TR ><TD ><TT CLASS="TYPE" >anyrange</TT ></TD ><TD >Indicates that a function accepts any range data type (see <A HREF="extend-type-system.html#EXTEND-TYPES-POLYMORPHIC" >Section 36.2.5</A > and <A HREF="rangetypes.html" >Section 8.17</A >).</TD ></TR ><TR ><TD ><TT CLASS="TYPE" >cstring</TT ></TD ><TD >Indicates that a function accepts or returns a null-terminated C string.</TD ></TR ><TR ><TD ><TT CLASS="TYPE" >internal</TT ></TD ><TD >Indicates that a function accepts or returns a server-internal data type.</TD ></TR ><TR ><TD ><TT CLASS="TYPE" >language_handler</TT ></TD ><TD >A procedural language call handler is declared to return <TT CLASS="TYPE" >language_handler</TT >.</TD ></TR ><TR ><TD ><TT CLASS="TYPE" >fdw_handler</TT ></TD ><TD >A foreign-data wrapper handler is declared to return <TT CLASS="TYPE" >fdw_handler</TT >.</TD ></TR ><TR ><TD ><TT CLASS="TYPE" >index_am_handler</TT ></TD ><TD >An index access method handler is declared to return <TT CLASS="TYPE" >index_am_handler</TT >.</TD ></TR ><TR ><TD ><TT CLASS="TYPE" >tsm_handler</TT ></TD ><TD >A tablesample method handler is declared to return <TT CLASS="TYPE" >tsm_handler</TT >.</TD ></TR ><TR ><TD ><TT CLASS="TYPE" >record</TT ></TD ><TD >Identifies a function taking or returning an unspecified row type.</TD ></TR ><TR ><TD ><TT CLASS="TYPE" >trigger</TT ></TD ><TD >A trigger function is declared to return <TT CLASS="TYPE" >trigger.</TT ></TD ></TR ><TR ><TD ><TT CLASS="TYPE" >event_trigger</TT ></TD ><TD >An event trigger function is declared to return <TT CLASS="TYPE" >event_trigger.</TT ></TD ></TR ><TR ><TD ><TT CLASS="TYPE" >pg_ddl_command</TT ></TD ><TD >Identifies a representation of DDL commands that is available to event triggers.</TD ></TR ><TR ><TD ><TT CLASS="TYPE" >void</TT ></TD ><TD >Indicates that a function returns no value.</TD ></TR ><TR ><TD ><TT CLASS="TYPE" >opaque</TT ></TD ><TD >An obsolete type name that formerly served all the above purposes.</TD ></TR ></TBODY ></TABLE ></DIV ><P > 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. </P ><P > 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 <TT CLASS="TYPE" >void</TT > and <TT CLASS="TYPE" >record</TT > as a result type (plus <TT CLASS="TYPE" >trigger</TT > or <TT CLASS="TYPE" >event_trigger</TT > when the function is used as a trigger or event trigger). Some also support polymorphic functions using the types <TT CLASS="TYPE" >anyelement</TT >, <TT CLASS="TYPE" >anyarray</TT >, <TT CLASS="TYPE" >anynonarray</TT >, <TT CLASS="TYPE" >anyenum</TT >, and <TT CLASS="TYPE" >anyrange</TT >. </P ><P > The <TT CLASS="TYPE" >internal</TT > 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 <ACRONYM CLASS="ACRONYM" >SQL</ACRONYM > query. If a function has at least one <TT CLASS="TYPE" >internal</TT >-type argument then it cannot be called from <ACRONYM CLASS="ACRONYM" >SQL</ACRONYM >. 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 <TT CLASS="TYPE" >internal</TT > unless it has at least one <TT CLASS="TYPE" >internal</TT > argument. </P ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE SUMMARY="Footer navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="datatype-pg-lsn.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="index.html" ACCESSKEY="H" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="functions.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><ACRONYM CLASS="ACRONYM" >pg_lsn Type</ACRONYM ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="datatype.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >Functions and Operators</TD ></TR ></TABLE ></DIV ></BODY ></HTML >