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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Chapter 36. The Information Schema</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets V1.79.1" /><link rel="prev" href="ecpg-develop.html" title="35.16. Internals" /><link rel="next" href="infoschema-schema.html" title="36.1. The Schema" /></head><body><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">Chapter 36. The Information Schema</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="ecpg-develop.html" title="35.16. Internals">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="client-interfaces.html" title="Part IV. Client Interfaces">Up</a></td><th width="60%" align="center">Part IV. Client Interfaces</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 12.4 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="infoschema-schema.html" title="36.1. The Schema">Next</a></td></tr></table><hr></hr></div><div class="chapter" id="INFORMATION-SCHEMA"><div class="titlepage"><div><div><h2 class="title">Chapter 36. The Information Schema</h2></div></div></div><div class="toc"><p><strong>Table of Contents</strong></p><dl class="toc"><dt><span class="sect1"><a href="infoschema-schema.html">36.1. The Schema</a></span></dt><dt><span class="sect1"><a href="infoschema-datatypes.html">36.2. Data Types</a></span></dt><dt><span class="sect1"><a href="infoschema-information-schema-catalog-name.html">36.3. <code class="literal">information_schema_catalog_name</code></a></span></dt><dt><span class="sect1"><a href="infoschema-administrable-role-authorizations.html">36.4. <code class="literal">administrable_role_authorizations</code></a></span></dt><dt><span class="sect1"><a href="infoschema-applicable-roles.html">36.5. <code class="literal">applicable_roles</code></a></span></dt><dt><span class="sect1"><a href="infoschema-attributes.html">36.6. <code class="literal">attributes</code></a></span></dt><dt><span class="sect1"><a href="infoschema-character-sets.html">36.7. <code class="literal">character_sets</code></a></span></dt><dt><span class="sect1"><a href="infoschema-check-constraint-routine-usage.html">36.8. <code class="literal">check_constraint_routine_usage</code></a></span></dt><dt><span class="sect1"><a href="infoschema-check-constraints.html">36.9. <code class="literal">check_constraints</code></a></span></dt><dt><span class="sect1"><a href="infoschema-collations.html">36.10. <code class="literal">collations</code></a></span></dt><dt><span class="sect1"><a href="infoschema-collation-character-set-applicab.html">36.11. <code class="literal">collation_character_set_applicability</code></a></span></dt><dt><span class="sect1"><a href="infoschema-column-column-usage.html">36.12. <code class="literal">column_column_usage</code></a></span></dt><dt><span class="sect1"><a href="infoschema-column-domain-usage.html">36.13. <code class="literal">column_domain_usage</code></a></span></dt><dt><span class="sect1"><a href="infoschema-column-options.html">36.14. <code class="literal">column_options</code></a></span></dt><dt><span class="sect1"><a href="infoschema-column-privileges.html">36.15. <code class="literal">column_privileges</code></a></span></dt><dt><span class="sect1"><a href="infoschema-column-udt-usage.html">36.16. <code class="literal">column_udt_usage</code></a></span></dt><dt><span class="sect1"><a href="infoschema-columns.html">36.17. <code class="literal">columns</code></a></span></dt><dt><span class="sect1"><a href="infoschema-constraint-column-usage.html">36.18. <code class="literal">constraint_column_usage</code></a></span></dt><dt><span class="sect1"><a href="infoschema-constraint-table-usage.html">36.19. <code class="literal">constraint_table_usage</code></a></span></dt><dt><span class="sect1"><a href="infoschema-data-type-privileges.html">36.20. <code class="literal">data_type_privileges</code></a></span></dt><dt><span class="sect1"><a href="infoschema-domain-constraints.html">36.21. <code class="literal">domain_constraints</code></a></span></dt><dt><span class="sect1"><a href="infoschema-domain-udt-usage.html">36.22. <code class="literal">domain_udt_usage</code></a></span></dt><dt><span class="sect1"><a href="infoschema-domains.html">36.23. <code class="literal">domains</code></a></span></dt><dt><span class="sect1"><a href="infoschema-element-types.html">36.24. <code class="literal">element_types</code></a></span></dt><dt><span class="sect1"><a href="infoschema-enabled-roles.html">36.25. <code class="literal">enabled_roles</code></a></span></dt><dt><span class="sect1"><a href="infoschema-foreign-data-wrapper-options.html">36.26. <code class="literal">foreign_data_wrapper_options</code></a></span></dt><dt><span class="sect1"><a href="infoschema-foreign-data-wrappers.html">36.27. <code class="literal">foreign_data_wrappers</code></a></span></dt><dt><span class="sect1"><a href="infoschema-foreign-server-options.html">36.28. <code class="literal">foreign_server_options</code></a></span></dt><dt><span class="sect1"><a href="infoschema-foreign-servers.html">36.29. <code class="literal">foreign_servers</code></a></span></dt><dt><span class="sect1"><a href="infoschema-foreign-table-options.html">36.30. <code class="literal">foreign_table_options</code></a></span></dt><dt><span class="sect1"><a href="infoschema-foreign-tables.html">36.31. <code class="literal">foreign_tables</code></a></span></dt><dt><span class="sect1"><a href="infoschema-key-column-usage.html">36.32. <code class="literal">key_column_usage</code></a></span></dt><dt><span class="sect1"><a href="infoschema-parameters.html">36.33. <code class="literal">parameters</code></a></span></dt><dt><span class="sect1"><a href="infoschema-referential-constraints.html">36.34. <code class="literal">referential_constraints</code></a></span></dt><dt><span class="sect1"><a href="infoschema-role-column-grants.html">36.35. <code class="literal">role_column_grants</code></a></span></dt><dt><span class="sect1"><a href="infoschema-role-routine-grants.html">36.36. <code class="literal">role_routine_grants</code></a></span></dt><dt><span class="sect1"><a href="infoschema-role-table-grants.html">36.37. <code class="literal">role_table_grants</code></a></span></dt><dt><span class="sect1"><a href="infoschema-role-udt-grants.html">36.38. <code class="literal">role_udt_grants</code></a></span></dt><dt><span class="sect1"><a href="infoschema-role-usage-grants.html">36.39. <code class="literal">role_usage_grants</code></a></span></dt><dt><span class="sect1"><a href="infoschema-routine-privileges.html">36.40. <code class="literal">routine_privileges</code></a></span></dt><dt><span class="sect1"><a href="infoschema-routines.html">36.41. <code class="literal">routines</code></a></span></dt><dt><span class="sect1"><a href="infoschema-schemata.html">36.42. <code class="literal">schemata</code></a></span></dt><dt><span class="sect1"><a href="infoschema-sequences.html">36.43. <code class="literal">sequences</code></a></span></dt><dt><span class="sect1"><a href="infoschema-sql-features.html">36.44. <code class="literal">sql_features</code></a></span></dt><dt><span class="sect1"><a href="infoschema-sql-implementation-info.html">36.45. <code class="literal">sql_implementation_info</code></a></span></dt><dt><span class="sect1"><a href="infoschema-sql-languages.html">36.46. <code class="literal">sql_languages</code></a></span></dt><dt><span class="sect1"><a href="infoschema-sql-packages.html">36.47. <code class="literal">sql_packages</code></a></span></dt><dt><span class="sect1"><a href="infoschema-sql-parts.html">36.48. <code class="literal">sql_parts</code></a></span></dt><dt><span class="sect1"><a href="infoschema-sql-sizing.html">36.49. <code class="literal">sql_sizing</code></a></span></dt><dt><span class="sect1"><a href="infoschema-sql-sizing-profiles.html">36.50. <code class="literal">sql_sizing_profiles</code></a></span></dt><dt><span class="sect1"><a href="infoschema-table-constraints.html">36.51. <code class="literal">table_constraints</code></a></span></dt><dt><span class="sect1"><a href="infoschema-table-privileges.html">36.52. <code class="literal">table_privileges</code></a></span></dt><dt><span class="sect1"><a href="infoschema-tables.html">36.53. <code class="literal">tables</code></a></span></dt><dt><span class="sect1"><a href="infoschema-transforms.html">36.54. <code class="literal">transforms</code></a></span></dt><dt><span class="sect1"><a href="infoschema-triggered-update-columns.html">36.55. <code class="literal">triggered_update_columns</code></a></span></dt><dt><span class="sect1"><a href="infoschema-triggers.html">36.56. <code class="literal">triggers</code></a></span></dt><dt><span class="sect1"><a href="infoschema-udt-privileges.html">36.57. <code class="literal">udt_privileges</code></a></span></dt><dt><span class="sect1"><a href="infoschema-usage-privileges.html">36.58. <code class="literal">usage_privileges</code></a></span></dt><dt><span class="sect1"><a href="infoschema-user-defined-types.html">36.59. <code class="literal">user_defined_types</code></a></span></dt><dt><span class="sect1"><a href="infoschema-user-mapping-options.html">36.60. <code class="literal">user_mapping_options</code></a></span></dt><dt><span class="sect1"><a href="infoschema-user-mappings.html">36.61. <code class="literal">user_mappings</code></a></span></dt><dt><span class="sect1"><a href="infoschema-view-column-usage.html">36.62. <code class="literal">view_column_usage</code></a></span></dt><dt><span class="sect1"><a href="infoschema-view-routine-usage.html">36.63. <code class="literal">view_routine_usage</code></a></span></dt><dt><span class="sect1"><a href="infoschema-view-table-usage.html">36.64. <code class="literal">view_table_usage</code></a></span></dt><dt><span class="sect1"><a href="infoschema-views.html">36.65. <code class="literal">views</code></a></span></dt></dl></div><a id="id-1.7.6.2" class="indexterm"></a><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 modeled 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"><h3 class="title">Note</h3><p>
   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 <code class="literal">check_constraint_routine_usage</code>,
   <code class="literal">check_constraints</code>, <code class="literal">domain_constraints</code>, and
   <code class="literal">referential_constraints</code>.  Some other views have similar
   issues but contain the table name to help distinguish duplicate
   rows, e.g., <code class="literal">constraint_column_usage</code>,
   <code class="literal">constraint_table_usage</code>, <code class="literal">table_constraints</code>.
  </p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="ecpg-develop.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="client-interfaces.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="infoschema-schema.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">35.16. Internals </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> 36.1. The Schema</td></tr></table></div></body></html>