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| <section id="predicate-functions"> |
| <h1>Predicate Functions<a class="headerlink" href="#predicate-functions" title="Permalink to this heading"></a></h1> |
| <p>Predicates are boolean functions that return true or false for a given set of input. They are most commonly used to filter out subgraphs in the WHERE part of a query.</p> |
| <section id="exists-property"> |
| <h2>Exists(Property)<a class="headerlink" href="#exists-property" title="Permalink to this heading"></a></h2> |
| <p><code class="docutils literal notranslate"><span class="pre">exists()</span></code> returns <code class="docutils literal notranslate"><span class="pre">true</span></code> if the specified property exists in the node, relationship or map. This is different from the <code class="docutils literal notranslate"><span class="pre">EXISTS</span></code> clause.</p> |
| <p>Syntax: <code class="docutils literal notranslate"><span class="pre">exists(property)</span></code></p> |
| <p>Returns:</p> |
| <p>An agtype boolean</p> |
| <p>Arguments:</p> |
| <table> |
| <tr> |
| <td>Name |
| </td> |
| <td>Description |
| </td> |
| </tr> |
| <tr> |
| <td>property |
| </td> |
| <td>A property from a vertex or edge |
| </td> |
| </tr> |
| </table> |
| <p>Query</p> |
| <div class="highlight-postgresql notranslate"><div class="highlight"><pre><span></span><span class="k">SELECT</span><span class="w"> </span><span class="o">*</span> |
| <span class="k">FROM</span><span class="w"> </span><span class="n">cypher</span><span class="p">(</span><span class="s1">'graph_name'</span><span class="p">,</span><span class="w"> </span><span class="s">$$</span> |
| <span class="s"> MATCH (n)</span> |
| <span class="s"> WHERE exists(n.surname)</span> |
| <span class="s"> RETURN n.first_name, n.last_name</span> |
| <span class="s">$$</span><span class="p">)</span><span class="w"> </span><span class="k">as</span><span class="w"> </span><span class="p">(</span><span class="n">first_name</span><span class="w"> </span><span class="n">agtype</span><span class="p">,</span><span class="w"> </span><span class="n">last_name</span><span class="w"> </span><span class="n">agtype</span><span class="p">);</span> |
| </pre></div> |
| </div> |
| <p>Results:</p> |
| <table> |
| <tr> |
| <td>first_name |
| </td> |
| <td>last_name |
| </td> |
| </tr> |
| <tr> |
| <td>‘John |
| </td> |
| <td>‘Smith’ |
| </td> |
| </tr> |
| <tr> |
| <td>‘Patty’ |
| </td> |
| <td>‘Patterson’ |
| </td> |
| </tr> |
| <tr> |
| <td colspan="2" >2 row(s) returned |
| </td> |
| </tr> |
| </table> |
| </section> |
| <section id="exists-path"> |
| <h2>Exists(Path)<a class="headerlink" href="#exists-path" title="Permalink to this heading"></a></h2> |
| <p><code class="docutils literal notranslate"><span class="pre">EXISTS(path)</span></code> returns <code class="docutils literal notranslate"><span class="pre">true</span></code> if for the given path, there already exists the given path.</p> |
| <div class="highlight-postgresql notranslate"><div class="highlight"><pre><span></span><span class="k">SELECT</span><span class="w"> </span><span class="o">*</span> |
| <span class="k">FROM</span><span class="w"> </span><span class="n">cypher</span><span class="p">(</span><span class="s1">'graph_name'</span><span class="p">,</span><span class="w"> </span><span class="s">$$</span> |
| <span class="s"> MATCH (n)</span> |
| <span class="s"> WHERE exists((n)-[]-({name: 'Willem Defoe'}))</span> |
| <span class="s"> RETURN n.full_name</span> |
| <span class="s">$$</span><span class="p">)</span><span class="w"> </span><span class="k">as</span><span class="w"> </span><span class="p">(</span><span class="n">full_name</span><span class="w"> </span><span class="n">agtype</span><span class="p">);</span> |
| </pre></div> |
| </div> |
| <p>Results:</p> |
| <table> |
| <tr> |
| <td>full_name |
| </td> |
| </tr> |
| <tr> |
| <td>‘Toby Maguire' |
| </td> |
| </tr> |
| <tr> |
| <td>‘Tom Holland’ |
| </td> |
| </tr> |
| <tr> |
| <td colspan="2" >2 row(s) returned |
| </td> |
| </tr> |
| </table> |
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