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<div class="section" id="examples-for-using-the-system-catalogs">
<h1>Examples for using the system catalogs<a class="headerlink" href="#examples-for-using-the-system-catalogs" title="Permalink to this headline">¶</a></h1>
<p>The system catalogs are regular tables where PostgreSQL stores schema metadata,
such as information about tables and columns, and internal bookkeeping
information. You can drop and recreate the tables, add columns, insert and
update values, and severely mess up your system that way. Normally, one
should not change the system catalogs by hand, there are always SQL commands
to do that. For example, CREATE DATABASE inserts a row into the <em>pg_database</em>
catalog — and actually creates the database on disk.</p>
<p>It this section we want to show examples for how to parse some of the system
catalogs, making queries with the classic PyGreSQL interface.</p>
<p>We assume that you have already created a connection to the PostgreSQL
database, as explained in the <a class="reference internal" href="basic.html"><span class="doc">Basic examples</span></a>:</p>
<div class="highlight-default"><div class="highlight"><pre><span class="gp">>>> </span><span class="kn">from</span> <span class="nn">pg</span> <span class="k">import</span> <span class="n">DB</span>
<span class="gp">>>> </span><span class="n">db</span> <span class="o">=</span> <span class="n">DB</span><span class="p">()</span>
<span class="gp">>>> </span><span class="n">query</span> <span class="o">=</span> <span class="n">query</span>
</pre></div>
</div>
<div class="section" id="lists-indices">
<h2>Lists indices<a class="headerlink" href="#lists-indices" title="Permalink to this headline">¶</a></h2>
<p>This query lists all simple indices in the database:</p>
<div class="highlight-default"><div class="highlight"><pre><span class="nb">print</span><span class="p">(</span><span class="n">query</span><span class="p">(</span><span class="s">"""SELECT bc.relname AS class_name,</span>
<span class="s"> ic.relname AS index_name, a.attname</span>
<span class="s"> FROM pg_class bc, pg_class ic, pg_index i, pg_attribute a</span>
<span class="s"> WHERE i.indrelid = bc.oid AND i.indexrelid = ic.oid</span>
<span class="s"> AND i.indkey[0] = a.attnum AND a.attrelid = bc.oid</span>
<span class="s"> AND NOT a.attisdropped</span>
<span class="s"> ORDER BY class_name, index_name, attname"""</span><span class="p">))</span>
</pre></div>
</div>
</div>
<div class="section" id="list-user-defined-attributes">
<h2>List user defined attributes<a class="headerlink" href="#list-user-defined-attributes" title="Permalink to this headline">¶</a></h2>
<p>This query lists all user defined attributes and their type
in user-defined classes:</p>
<div class="highlight-default"><div class="highlight"><pre><span class="nb">print</span><span class="p">(</span><span class="n">query</span><span class="p">(</span><span class="s">"""SELECT c.relname, a.attname, t.typname</span>
<span class="s"> FROM pg_class c, pg_attribute a, pg_type t</span>
<span class="s"> WHERE c.relkind = 'r' and c.relname !~ '^pg_'</span>
<span class="s"> AND c.relname !~ '^Inv' and a.attnum > 0</span>
<span class="s"> AND a.attrelid = c.oid and a.atttypid = t.oid</span>
<span class="s"> AND NOT a.attisdropped</span>
<span class="s"> ORDER BY relname, attname"""</span><span class="p">))</span>
</pre></div>
</div>
</div>
<div class="section" id="list-user-defined-base-types">
<h2>List user defined base types<a class="headerlink" href="#list-user-defined-base-types" title="Permalink to this headline">¶</a></h2>
<p>This query lists all user defined base types:</p>
<div class="highlight-default"><div class="highlight"><pre><span class="nb">print</span><span class="p">(</span><span class="n">query</span><span class="p">(</span><span class="s">"""SELECT r.rolname, t.typname</span>
<span class="s"> FROM pg_type t, pg_authid r</span>
<span class="s"> WHERE r.oid = t.typowner</span>
<span class="s"> AND t.typrelid = '0'::oid and t.typelem = '0'::oid</span>
<span class="s"> AND r.rolname != 'postgres'</span>
<span class="s"> ORDER BY rolname, typname"""</span><span class="p">))</span>
</pre></div>
</div>
</div>
<div class="section" id="list-operators">
<h2>List operators<a class="headerlink" href="#list-operators" title="Permalink to this headline">¶</a></h2>
<p>This query lists all right-unary operators:</p>
<div class="highlight-default"><div class="highlight"><pre><span class="nb">print</span><span class="p">(</span><span class="n">query</span><span class="p">(</span><span class="s">"""SELECT o.oprname AS right_unary,</span>
<span class="s"> lt.typname AS operand, result.typname AS return_type</span>
<span class="s"> FROM pg_operator o, pg_type lt, pg_type result</span>
<span class="s"> WHERE o.oprkind='r' and o.oprleft = lt.oid</span>
<span class="s"> AND o.oprresult = result.oid</span>
<span class="s"> ORDER BY operand"""</span><span class="p">))</span>
</pre></div>
</div>
<p>This query lists all left-unary operators:</p>
<div class="highlight-default"><div class="highlight"><pre><span class="nb">print</span><span class="p">(</span><span class="n">query</span><span class="p">(</span><span class="s">"""SELECT o.oprname AS left_unary,</span>
<span class="s"> rt.typname AS operand, result.typname AS return_type</span>
<span class="s"> FROM pg_operator o, pg_type rt, pg_type result</span>
<span class="s"> WHERE o.oprkind='l' AND o.oprright = rt.oid</span>
<span class="s"> AND o.oprresult = result.oid</span>
<span class="s"> ORDER BY operand"""</span><span class="p">))</span>
</pre></div>
</div>
<p>And this one lists all of the binary operators:</p>
<div class="highlight-default"><div class="highlight"><pre><span class="nb">print</span><span class="p">(</span><span class="n">query</span><span class="p">(</span><span class="s">"""SELECT o.oprname AS binary_op,</span>
<span class="s"> rt.typname AS right_opr, lt.typname AS left_opr,</span>
<span class="s"> result.typname AS return_type</span>
<span class="s"> FROM pg_operator o, pg_type rt, pg_type lt, pg_type result</span>
<span class="s"> WHERE o.oprkind = 'b' AND o.oprright = rt.oid</span>
<span class="s"> AND o.oprleft = lt.oid AND o.oprresult = result.oid"""</span><span class="p">))</span>
</pre></div>
</div>
</div>
<div class="section" id="list-functions-of-a-language">
<h2>List functions of a language<a class="headerlink" href="#list-functions-of-a-language" title="Permalink to this headline">¶</a></h2>
<p>Given a programming language, this query returns the name, args and return
type from all functions of a language:</p>
<div class="highlight-default"><div class="highlight"><pre><span class="n">language</span> <span class="o">=</span> <span class="s">'sql'</span>
<span class="nb">print</span><span class="p">(</span><span class="n">query</span><span class="p">(</span><span class="s">"""SELECT p.proname, p.pronargs, t.typname</span>
<span class="s"> FROM pg_proc p, pg_language l, pg_type t</span>
<span class="s"> WHERE p.prolang = l.oid AND p.prorettype = t.oid</span>
<span class="s"> AND l.lanname = $1</span>
<span class="s"> ORDER BY proname"""</span><span class="p">,</span> <span class="p">(</span><span class="n">language</span><span class="p">,)))</span>
</pre></div>
</div>
</div>
<div class="section" id="list-aggregate-functions">
<h2>List aggregate functions<a class="headerlink" href="#list-aggregate-functions" title="Permalink to this headline">¶</a></h2>
<p>This query lists all of the aggregate functions and the type to which
they can be applied:</p>
<div class="highlight-default"><div class="highlight"><pre><span class="nb">print</span><span class="p">(</span><span class="n">query</span><span class="p">(</span><span class="s">"""SELECT p.proname, t.typname</span>
<span class="s"> FROM pg_aggregate a, pg_proc p, pg_type t</span>
<span class="s"> WHERE a.aggfnoid = p.oid</span>
<span class="s"> and p.proargtypes[0] = t.oid</span>
<span class="s"> ORDER BY proname, typname"""</span><span class="p">))</span>
</pre></div>
</div>
</div>
<div class="section" id="list-operator-families">
<h2>List operator families<a class="headerlink" href="#list-operator-families" title="Permalink to this headline">¶</a></h2>
<p>The following query lists all defined operator families and all the operators
included in each family:</p>
<div class="highlight-default"><div class="highlight"><pre><span class="nb">print</span><span class="p">(</span><span class="n">query</span><span class="p">(</span><span class="s">"""SELECT am.amname, opf.opfname, amop.amopopr::regoperator</span>
<span class="s"> FROM pg_am am, pg_opfamily opf, pg_amop amop</span>
<span class="s"> WHERE opf.opfmethod = am.oid</span>
<span class="s"> AND amop.amopfamily = opf.oid</span>
<span class="s"> ORDER BY amname, opfname, amopopr"""</span><span class="p">))</span>
</pre></div>
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<h3><a href="../../index.html">Page contents</a></h3>
<ul>
<li><a class="reference internal" href="#">Examples for using the system catalogs</a><ul>
<li><a class="reference internal" href="#lists-indices">Lists indices</a></li>
<li><a class="reference internal" href="#list-user-defined-attributes">List user defined attributes</a></li>
<li><a class="reference internal" href="#list-user-defined-base-types">List user defined base types</a></li>
<li><a class="reference internal" href="#list-operators">List operators</a></li>
<li><a class="reference internal" href="#list-functions-of-a-language">List functions of a language</a></li>
<li><a class="reference internal" href="#list-aggregate-functions">List aggregate functions</a></li>
<li><a class="reference internal" href="#list-operator-families">List operator families</a></li>
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