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<title>pg_foreign_data_wrapper</title>
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<p>The system catalog table <codeph>pg_foreign_data_wrapper</codeph> stores foreign-data wrapper definitions. A foreign-data wrapper is a mechanism by which you access external data residing on foreign servers.</p>
<entrycolname="col4">A reference to a handler function that is responsible for supplying execution routines for the foreign-data wrapper. Zero if no handler is provided.</entry>
<entrycolname="col4">A reference to a validator function that is responsible for checking the validity of the options provided to the foreign-data wrapper. This function also checks the options for foreign servers and user mappings using the foreign-data wrapper. Zero if no validator is provided.</entry>
<entrycolname="col4">Access privileges; see <codeph><xrefhref="../sql_commands/GRANT.xml#topic1"type="topic"format="dita"/></codeph> and <codeph><xrefhref="../sql_commands/REVOKE.xml#topic1"type="topic"format="dita"/></codeph> for details.</entry>
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<title>pg_foreign_server</title>
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<p>The system catalog table <codeph>pg_foreign_server</codeph> stores foreign server definitions. A foreign server describes a source of external data, such as a remote server. You access a foreign server via a foreign-data wrapper.</p>
<entrycolname="col4">Access privileges; see <codeph><xrefhref="../sql_commands/GRANT.xml#topic1"type="topic"format="dita"/></codeph> and <codeph><xrefhref="../sql_commands/REVOKE.xml#topic1"type="topic"format="dita"/></codeph> for details.</entry>
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<title>pg_foreign_table</title>
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<p>The system catalog table <codeph>pg_foreign_table</codeph> contains auxiliary information about foreign tables. A foreign table is primarily represented by a <codeph>pg_class</codeph> entry, just like a regular table. Its <codeph>pg_foreign_table</codeph> entry contains the information that is pertinent only to foreign tables and not any other kind of relation.</p>
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<topicid="topic1"xml:lang="en"><titleid="ib138336">pg_user_mapping</title><body><p>The <codeph>pg_user_mapping</codeph> catalog table stores the mappings from local users to remote
users. You must have administrator privileges to view this catalog.</p><tableid="ib138428"><title>pg_catalog.pg_user_mapping</title><tgroupcols="4"><colspeccolnum="1"colname="col1"colwidth="83pt"/><colspeccolnum="2"colname="col2"colwidth="60pt"/><colspeccolnum="3"colname="col3"colwidth="99pt"/><colspeccolnum="4"colname="col4"colwidth="205pt"/><thead><row><entrycolname="col1">column</entry><entrycolname="col2">type</entry><entrycolname="col3">references</entry><entrycolname="col4">description</entry></row></thead><tbody><row><entrycolname="col1"><codephid="ib138551">umuser</codeph></entry><entrycolname="col2">oid</entry><entrycolname="col3">pg_authid.oid</entry><entrycolname="col4">OID of the local role being mapped, 0 if the
user mapping is public</entry></row><row><entrycolname="col1"><codephid="ib138559">umserver</codeph></entry><entrycolname="col2">oid</entry><entrycolname="col3">pg_foreign_server.oid</entry><entrycolname="col4">The OID of the foreign server that contains
this mapping </entry></row><row><entrycolname="col1"><codephid="ib138567">umoptions</codeph></entry><entrycolname="col2">text [ ]</entry><entrycolname="col3"/><entrycolname="col4">User mapping specific options, as "keyword=value"
<p>The system catalog table <codeph>pg_user_mapping</codeph> stores the mappings from local user to remote user. You must have administrator privileges to view this catalog. Access to this catalog is restricted from normal users, use the <codeph>pg_user_mappings</codeph> view instead.</p>