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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <HTML ><HEAD ><TITLE >The Information Schema</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 9.2.24 Documentation" HREF="index.html"><LINK REL="UP" TITLE="Client Interfaces" HREF="client-interfaces.html"><LINK REL="PREVIOUS" TITLE="Internals" HREF="ecpg-develop.html"><LINK REL="NEXT" TITLE="The Schema" HREF="infoschema-schema.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="2017-11-06T22:43:11"></HEAD ><BODY CLASS="CHAPTER" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="5" ALIGN="center" VALIGN="bottom" ><A HREF="index.html" >PostgreSQL 9.2.24 Documentation</A ></TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A TITLE="Internals" HREF="ecpg-develop.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A HREF="client-interfaces.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="60%" ALIGN="center" VALIGN="bottom" ></TD ><TD WIDTH="20%" ALIGN="right" VALIGN="top" ><A TITLE="The Schema" HREF="infoschema-schema.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="CHAPTER" ><H1 ><A NAME="INFORMATION-SCHEMA" ></A >Chapter 34. The Information Schema</H1 ><DIV CLASS="TOC" ><DL ><DT ><B >Table of Contents</B ></DT ><DT >34.1. <A HREF="infoschema-schema.html" >The Schema</A ></DT ><DT >34.2. <A HREF="infoschema-datatypes.html" >Data Types</A ></DT ><DT >34.3. <A HREF="infoschema-information-schema-catalog-name.html" ><TT CLASS="LITERAL" >information_schema_catalog_name</TT ></A ></DT ><DT >34.4. <A HREF="infoschema-administrable-role-authorizations.html" ><TT CLASS="LITERAL" >administrable_role_authorizations</TT ></A ></DT ><DT >34.5. <A HREF="infoschema-applicable-roles.html" ><TT CLASS="LITERAL" >applicable_roles</TT ></A ></DT ><DT >34.6. <A HREF="infoschema-attributes.html" ><TT CLASS="LITERAL" >attributes</TT ></A ></DT ><DT >34.7. <A HREF="infoschema-character-sets.html" ><TT CLASS="LITERAL" >character_sets</TT ></A ></DT ><DT >34.8. <A HREF="infoschema-check-constraint-routine-usage.html" ><TT CLASS="LITERAL" >check_constraint_routine_usage</TT ></A ></DT ><DT >34.9. <A HREF="infoschema-check-constraints.html" ><TT CLASS="LITERAL" >check_constraints</TT ></A ></DT ><DT >34.10. <A HREF="infoschema-collations.html" ><TT CLASS="LITERAL" >collations</TT ></A ></DT ><DT >34.11. <A HREF="infoschema-collation-character-set-applicab.html" ><TT CLASS="LITERAL" >collation_character_set_applicability</TT ></A ></DT ><DT >34.12. <A HREF="infoschema-column-domain-usage.html" ><TT CLASS="LITERAL" >column_domain_usage</TT ></A ></DT ><DT >34.13. <A HREF="infoschema-column-options.html" ><TT CLASS="LITERAL" >column_options</TT ></A ></DT ><DT >34.14. <A HREF="infoschema-column-privileges.html" ><TT CLASS="LITERAL" >column_privileges</TT ></A ></DT ><DT >34.15. <A HREF="infoschema-column-udt-usage.html" ><TT CLASS="LITERAL" >column_udt_usage</TT ></A ></DT ><DT >34.16. <A HREF="infoschema-columns.html" ><TT CLASS="LITERAL" >columns</TT ></A ></DT ><DT >34.17. <A HREF="infoschema-constraint-column-usage.html" ><TT CLASS="LITERAL" >constraint_column_usage</TT ></A ></DT ><DT >34.18. <A HREF="infoschema-constraint-table-usage.html" ><TT CLASS="LITERAL" >constraint_table_usage</TT ></A ></DT ><DT >34.19. <A HREF="infoschema-data-type-privileges.html" ><TT CLASS="LITERAL" >data_type_privileges</TT ></A ></DT ><DT >34.20. <A HREF="infoschema-domain-constraints.html" ><TT CLASS="LITERAL" >domain_constraints</TT ></A ></DT ><DT >34.21. <A HREF="infoschema-domain-udt-usage.html" ><TT CLASS="LITERAL" >domain_udt_usage</TT ></A ></DT ><DT >34.22. <A HREF="infoschema-domains.html" ><TT CLASS="LITERAL" >domains</TT ></A ></DT ><DT >34.23. <A HREF="infoschema-element-types.html" ><TT CLASS="LITERAL" >element_types</TT ></A ></DT ><DT >34.24. <A HREF="infoschema-enabled-roles.html" ><TT CLASS="LITERAL" >enabled_roles</TT ></A ></DT ><DT >34.25. <A HREF="infoschema-foreign-data-wrapper-options.html" ><TT CLASS="LITERAL" >foreign_data_wrapper_options</TT ></A ></DT ><DT >34.26. <A HREF="infoschema-foreign-data-wrappers.html" ><TT CLASS="LITERAL" >foreign_data_wrappers</TT ></A ></DT ><DT >34.27. <A HREF="infoschema-foreign-server-options.html" ><TT CLASS="LITERAL" >foreign_server_options</TT ></A ></DT ><DT >34.28. <A HREF="infoschema-foreign-servers.html" ><TT CLASS="LITERAL" >foreign_servers</TT ></A ></DT ><DT >34.29. <A HREF="infoschema-foreign-table-options.html" ><TT CLASS="LITERAL" >foreign_table_options</TT ></A ></DT ><DT >34.30. <A HREF="infoschema-foreign-tables.html" ><TT CLASS="LITERAL" >foreign_tables</TT ></A ></DT ><DT >34.31. <A HREF="infoschema-key-column-usage.html" ><TT CLASS="LITERAL" >key_column_usage</TT ></A ></DT ><DT >34.32. <A HREF="infoschema-parameters.html" ><TT CLASS="LITERAL" >parameters</TT ></A ></DT ><DT >34.33. <A HREF="infoschema-referential-constraints.html" ><TT CLASS="LITERAL" >referential_constraints</TT ></A ></DT ><DT >34.34. <A HREF="infoschema-role-column-grants.html" ><TT CLASS="LITERAL" >role_column_grants</TT ></A ></DT ><DT >34.35. <A HREF="infoschema-role-routine-grants.html" ><TT CLASS="LITERAL" >role_routine_grants</TT ></A ></DT ><DT >34.36. <A HREF="infoschema-role-table-grants.html" ><TT CLASS="LITERAL" >role_table_grants</TT ></A ></DT ><DT >34.37. <A HREF="infoschema-role-udt-grants.html" ><TT CLASS="LITERAL" >role_udt_grants</TT ></A ></DT ><DT >34.38. <A HREF="infoschema-role-usage-grants.html" ><TT CLASS="LITERAL" >role_usage_grants</TT ></A ></DT ><DT >34.39. <A HREF="infoschema-routine-privileges.html" ><TT CLASS="LITERAL" >routine_privileges</TT ></A ></DT ><DT >34.40. <A HREF="infoschema-routines.html" ><TT CLASS="LITERAL" >routines</TT ></A ></DT ><DT >34.41. <A HREF="infoschema-schemata.html" ><TT CLASS="LITERAL" >schemata</TT ></A ></DT ><DT >34.42. <A HREF="infoschema-sequences.html" ><TT CLASS="LITERAL" >sequences</TT ></A ></DT ><DT >34.43. <A HREF="infoschema-sql-features.html" ><TT CLASS="LITERAL" >sql_features</TT ></A ></DT ><DT >34.44. <A HREF="infoschema-sql-implementation-info.html" ><TT CLASS="LITERAL" >sql_implementation_info</TT ></A ></DT ><DT >34.45. <A HREF="infoschema-sql-languages.html" ><TT CLASS="LITERAL" >sql_languages</TT ></A ></DT ><DT >34.46. <A HREF="infoschema-sql-packages.html" ><TT CLASS="LITERAL" >sql_packages</TT ></A ></DT ><DT >34.47. <A HREF="infoschema-sql-parts.html" ><TT CLASS="LITERAL" >sql_parts</TT ></A ></DT ><DT >34.48. <A HREF="infoschema-sql-sizing.html" ><TT CLASS="LITERAL" >sql_sizing</TT ></A ></DT ><DT >34.49. <A HREF="infoschema-sql-sizing-profiles.html" ><TT CLASS="LITERAL" >sql_sizing_profiles</TT ></A ></DT ><DT >34.50. <A HREF="infoschema-table-constraints.html" ><TT CLASS="LITERAL" >table_constraints</TT ></A ></DT ><DT >34.51. <A HREF="infoschema-table-privileges.html" ><TT CLASS="LITERAL" >table_privileges</TT ></A ></DT ><DT >34.52. <A HREF="infoschema-tables.html" ><TT CLASS="LITERAL" >tables</TT ></A ></DT ><DT >34.53. <A HREF="infoschema-triggered-update-columns.html" ><TT CLASS="LITERAL" >triggered_update_columns</TT ></A ></DT ><DT >34.54. <A HREF="infoschema-triggers.html" ><TT CLASS="LITERAL" >triggers</TT ></A ></DT ><DT >34.55. <A HREF="infoschema-udt-privileges.html" ><TT CLASS="LITERAL" >udt_privileges</TT ></A ></DT ><DT >34.56. <A HREF="infoschema-usage-privileges.html" ><TT CLASS="LITERAL" >usage_privileges</TT ></A ></DT ><DT >34.57. <A HREF="infoschema-user-defined-types.html" ><TT CLASS="LITERAL" >user_defined_types</TT ></A ></DT ><DT >34.58. <A HREF="infoschema-user-mapping-options.html" ><TT CLASS="LITERAL" >user_mapping_options</TT ></A ></DT ><DT >34.59. <A HREF="infoschema-user-mappings.html" ><TT CLASS="LITERAL" >user_mappings</TT ></A ></DT ><DT >34.60. <A HREF="infoschema-view-column-usage.html" ><TT CLASS="LITERAL" >view_column_usage</TT ></A ></DT ><DT >34.61. <A HREF="infoschema-view-routine-usage.html" ><TT CLASS="LITERAL" >view_routine_usage</TT ></A ></DT ><DT >34.62. <A HREF="infoschema-view-table-usage.html" ><TT CLASS="LITERAL" >view_table_usage</TT ></A ></DT ><DT >34.63. <A HREF="infoschema-views.html" ><TT CLASS="LITERAL" >views</TT ></A ></DT ></DL ></DIV ><P > The information schema consists of a set of views that contain information about the objects defined in the current database. The information schema is defined in the SQL standard and can therefore be expected to be portable and remain stable — unlike the system catalogs, which are specific to <SPAN CLASS="PRODUCTNAME" >PostgreSQL</SPAN > and are modelled after implementation concerns. The information schema views do not, however, contain information about <SPAN CLASS="PRODUCTNAME" >PostgreSQL</SPAN >-specific features; to inquire about those you need to query the system catalogs or other <SPAN CLASS="PRODUCTNAME" >PostgreSQL</SPAN >-specific views. </P ><DIV CLASS="NOTE" ><BLOCKQUOTE CLASS="NOTE" ><P ><B >Note: </B > When querying the database for constraint information, it is possible for a standard-compliant query that expects to return one row to return several. This is because the SQL standard requires constraint names to be unique within a schema, but <SPAN CLASS="PRODUCTNAME" >PostgreSQL</SPAN > does not enforce this restriction. <SPAN CLASS="PRODUCTNAME" >PostgreSQL</SPAN > automatically-generated constraint names avoid duplicates in the same schema, but users can specify such duplicate names. </P ><P > This problem can appear when querying information schema views such as <TT CLASS="LITERAL" >check_constraint_routine_usage</TT >, <TT CLASS="LITERAL" >check_constraints</TT >, <TT CLASS="LITERAL" >domain_constraints</TT >, and <TT CLASS="LITERAL" >referential_constraints</TT >. Some other views have similar issues but contain the table name to help distinguish duplicate rows, e.g., <TT CLASS="LITERAL" >constraint_column_usage</TT >, <TT CLASS="LITERAL" >constraint_table_usage</TT >, <TT CLASS="LITERAL" >table_constraints</TT >. </P ></BLOCKQUOTE ></DIV ></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="ecpg-develop.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="infoschema-schema.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >Internals</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="client-interfaces.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >The Schema</TD ></TR ></TABLE ></DIV ></BODY ></HTML >