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<div class="section" id="examples-for-advanced-features">
<h1>Examples for advanced features<a class="headerlink" href="#examples-for-advanced-features" title="Permalink to this headline">¶</a></h1>
<p>In this section, we show how to use some advanced features of PostgreSQL
using 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="inheritance">
<h2>Inheritance<a class="headerlink" href="#inheritance" title="Permalink to this headline">¶</a></h2>
<p>A table can inherit from zero or more tables. A query can reference either
all rows of a table or all rows of a table plus all of its descendants.</p>
<p>For example, the capitals table inherits from cities table (it inherits
all data fields from cities):</p>
<div class="highlight-default"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">data</span> <span class="o">=</span> <span class="p">[(</span><span class="s">'cities'</span><span class="p">,</span> <span class="p">[</span>
<span class="gp">... </span> <span class="s">"'San Francisco', 7.24E+5, 63"</span><span class="p">,</span>
<span class="gp">... </span> <span class="s">"'Las Vegas', 2.583E+5, 2174"</span><span class="p">,</span>
<span class="gp">... </span> <span class="s">"'Mariposa', 1200, 1953"</span><span class="p">]),</span>
<span class="gp">... </span> <span class="p">(</span><span class="s">'capitals'</span><span class="p">,</span> <span class="p">[</span>
<span class="gp">... </span> <span class="s">"'Sacramento',3.694E+5,30,'CA'"</span><span class="p">,</span>
<span class="gp">... </span> <span class="s">"'Madison', 1.913E+5, 845, 'WI'"</span><span class="p">])]</span>
</pre></div>
</div>
<p>Now, let’s populate the tables:</p>
<div class="highlight-default"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">data</span> <span class="o">=</span> <span class="p">[</span><span class="s">'cities'</span><span class="p">,</span> <span class="p">[</span>
<span class="gp">... </span> <span class="s">"'San Francisco', 7.24E+5, 63"</span>
<span class="gp">... </span> <span class="s">"'Las Vegas', 2.583E+5, 2174"</span>
<span class="gp">... </span> <span class="s">"'Mariposa', 1200, 1953"</span><span class="p">],</span>
<span class="gp">... </span> <span class="s">'capitals'</span><span class="p">,</span> <span class="p">[</span>
<span class="gp">... </span> <span class="s">"'Sacramento',3.694E+5,30,'CA'"</span><span class="p">,</span>
<span class="gp">... </span> <span class="s">"'Madison', 1.913E+5, 845, 'WI'"</span><span class="p">]]</span>
<span class="gp">>>> </span><span class="k">for</span> <span class="n">table</span><span class="p">,</span> <span class="n">rows</span> <span class="ow">in</span> <span class="n">data</span><span class="p">:</span>
<span class="gp">... </span> <span class="k">for</span> <span class="n">row</span> <span class="ow">in</span> <span class="n">rows</span><span class="p">:</span>
<span class="gp">... </span> <span class="n">query</span><span class="p">(</span><span class="s">"INSERT INTO %s VALUES (%s)"</span> <span class="o">%</span> <span class="p">(</span><span class="n">table</span><span class="p">,</span> <span class="n">row</span><span class="p">))</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">query</span><span class="p">(</span><span class="s">"SELECT * FROM cities"</span><span class="p">))</span>
<span class="go"> name |population|altitude</span>
<span class="go">-------------+----------+--------</span>
<span class="go">San Francisco| 724000| 63</span>
<span class="go">Las Vegas | 258300| 2174</span>
<span class="go">Mariposa | 1200| 1953</span>
<span class="go">Sacramento | 369400| 30</span>
<span class="go">Madison | 191300| 845</span>
<span class="go">(5 rows)</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">query</span><span class="p">(</span><span class="s">"SELECT * FROM capitals"</span><span class="p">))</span>
<span class="go"> name |population|altitude|state</span>
<span class="go">----------+----------+--------+-----</span>
<span class="go">Sacramento| 369400| 30|CA</span>
<span class="go">Madison | 191300| 845|WI</span>
<span class="go">(2 rows)</span>
</pre></div>
</div>
<p>You can find all cities, including capitals, that are located at an altitude
of 500 feet or higher by:</p>
<div class="highlight-default"><div class="highlight"><pre><span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">query</span><span class="p">(</span><span class="s">"""SELECT c.name, c.altitude</span>
<span class="gp">... </span><span class="s"> FROM cities</span>
<span class="gp">... </span><span class="s"> WHERE altitude > 500"""</span><span class="p">))</span>
<span class="go"> name |altitude</span>
<span class="go">---------+--------</span>
<span class="go">Las Vegas| 2174</span>
<span class="go">Mariposa | 1953</span>
<span class="go">Madison | 845</span>
<span class="go">(3 rows)</span>
</pre></div>
</div>
<p>On the other hand, the following query references rows of the base table only,
i.e. it finds all cities that are not state capitals and are situated at an
altitude of 500 feet or higher:</p>
<div class="highlight-default"><div class="highlight"><pre><span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">query</span><span class="p">(</span><span class="s">"""SELECT name, altitude</span>
<span class="gp">... </span><span class="s"> FROM ONLY cities</span>
<span class="gp">... </span><span class="s"> WHERE altitude > 500"""</span><span class="p">))</span>
<span class="go"> name |altitude</span>
<span class="go">---------+--------</span>
<span class="go">Las Vegas| 2174</span>
<span class="go">Mariposa | 1953</span>
<span class="go">(2 rows)</span>
</pre></div>
</div>
</div>
<div class="section" id="arrays">
<h2>Arrays<a class="headerlink" href="#arrays" title="Permalink to this headline">¶</a></h2>
<p>Attributes can be arrays of base types or user-defined types:</p>
<div class="highlight-default"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">query</span><span class="p">(</span><span class="s">"""CREATE TABLE sal_emp (</span>
<span class="gp">... </span><span class="s"> name text,</span>
<span class="gp">... </span><span class="s"> pay_by_quarter int4[],</span>
<span class="gp">... </span><span class="s"> pay_by_extra_quarter int8[],</span>
<span class="gp">... </span><span class="s"> schedule text[][])"""</span><span class="p">)</span>
</pre></div>
</div>
<p>Insert instances with array attributes. Note the use of braces:</p>
<div class="highlight-default"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">query</span><span class="p">(</span><span class="s">"""INSERT INTO sal_emp VALUES (</span>
<span class="gp">... </span><span class="s"> 'Bill', '{10000,10000,10000,10000}',</span>
<span class="gp">... </span><span class="s"> '{9223372036854775800,9223372036854775800,9223372036854775800}',</span>
<span class="gp">... </span><span class="s"> '{{"meeting", "lunch"}, {"training", "presentation"}}')"""</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">query</span><span class="p">(</span><span class="s">"""INSERT INTO sal_emp VALUES (</span>
<span class="gp">... </span><span class="s"> 'Carol', '{20000,25000,25000,25000}',</span>
<span class="gp">... </span><span class="s"> '{9223372036854775807,9223372036854775807,9223372036854775807}',</span>
<span class="gp">... </span><span class="s"> '{{"breakfast", "consulting"}, {"meeting", "lunch"}}')"""</span><span class="p">)</span>
</pre></div>
</div>
<p>Queries on array attributes:</p>
<div class="highlight-default"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">query</span><span class="p">(</span><span class="s">"""SELECT name FROM sal_emp WHERE</span>
<span class="gp">... </span><span class="s"> sal_emp.pay_by_quarter[1] != sal_emp.pay_by_quarter[2]"""</span><span class="p">)</span>
<span class="go">name</span>
<span class="go">-----</span>
<span class="go">Carol</span>
<span class="go">(1 row)</span>
</pre></div>
</div>
<p>Retrieve third quarter pay of all employees:</p>
<div class="highlight-default"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">query</span><span class="p">(</span><span class="s">"SELECT sal_emp.pay_by_quarter[3] FROM sal_emp"</span><span class="p">)</span>
<span class="go">pay_by_quarter</span>
<span class="go">--------------</span>
<span class="go"> 10000</span>
<span class="go"> 25000</span>
<span class="go">(2 rows)</span>
</pre></div>
</div>
<p>Retrieve third quarter extra pay of all employees:</p>
<div class="highlight-default"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">query</span><span class="p">(</span><span class="s">"SELECT sal_emp.pay_by_extra_quarter[3] FROM sal_emp"</span><span class="p">)</span>
<span class="go">pay_by_extra_quarter</span>
<span class="go">--------------------</span>
<span class="go"> 9223372036854775800</span>
<span class="go"> 9223372036854775807</span>
<span class="go">(2 rows)</span>
</pre></div>
</div>
<p>Retrieve first two quarters of extra quarter pay of all employees:</p>
<div class="highlight-default"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">query</span><span class="p">(</span><span class="s">"SELECT sal_emp.pay_by_extra_quarter[1:2] FROM sal_emp"</span><span class="p">)</span>
<span class="go"> pay_by_extra_quarter</span>
<span class="go">-----------------------------------------</span>
<span class="go">{9223372036854775800,9223372036854775800}</span>
<span class="go">{9223372036854775807,9223372036854775807}</span>
<span class="go">(2 rows)</span>
</pre></div>
</div>
<p>Select subarrays:</p>
<div class="highlight-default"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">query</span><span class="p">(</span><span class="s">"""SELECT sal_emp.schedule[1:2][1:1] FROM sal_emp</span>
<span class="gp">... </span><span class="s"> WHERE sal_emp.name = 'Bill'"""</span><span class="p">)</span>
<span class="go"> schedule</span>
<span class="go">----------------------</span>
<span class="go">{{meeting},{training}}</span>
<span class="go">(1 row)</span>
</pre></div>
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