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| <div class="section" id="materialized-views"> |
| <span id="id1"></span><h1>Materialized Views<a class="headerlink" href="#materialized-views" title="Permalink to this headline">¶</a></h1> |
| <p>Materialized views names are defined by:</p> |
| <pre> |
| <strong id="grammar-token-view_name">view_name</strong> ::= re('[a-zA-Z_0-9]+') |
| </pre> |
| <div class="section" id="create-materialized-view"> |
| <span id="create-materialized-view-statement"></span><h2>CREATE MATERIALIZED VIEW<a class="headerlink" href="#create-materialized-view" title="Permalink to this headline">¶</a></h2> |
| <p>You can create a materialized view on a table using a <code class="docutils literal"><span class="pre">CREATE</span> <span class="pre">MATERIALIZED</span> <span class="pre">VIEW</span></code> statement:</p> |
| <pre> |
| <strong id="grammar-token-create_materialized_view_statement">create_materialized_view_statement</strong> ::= CREATE MATERIALIZED VIEW [ IF NOT EXISTS ] <a class="reference internal" href="#grammar-token-view_name"><code class="xref docutils literal"><span class="pre">view_name</span></code></a> AS |
| <a class="reference internal" href="dml.html#grammar-token-select_statement"><code class="xref docutils literal"><span class="pre">select_statement</span></code></a> |
| PRIMARY KEY '(' <a class="reference internal" href="ddl.html#grammar-token-primary_key"><code class="xref docutils literal"><span class="pre">primary_key</span></code></a> ')' |
| WITH <a class="reference internal" href="ddl.html#grammar-token-table_options"><code class="xref docutils literal"><span class="pre">table_options</span></code></a> |
| </pre> |
| <p>For instance:</p> |
| <div class="highlight-cql"><div class="highlight"><pre><span></span><span class="k">CREATE</span> <span class="k">MATERIALIZED</span> <span class="k">VIEW</span> <span class="n">monkeySpecies_by_population</span> <span class="k">AS</span> |
| <span class="k">SELECT</span> <span class="o">*</span> <span class="k">FROM</span> <span class="n">monkeySpecies</span> |
| <span class="k">WHERE</span> <span class="n">population</span> <span class="k">IS</span> <span class="k">NOT</span> <span class="k">NULL</span> <span class="k">AND</span> <span class="n">species</span> <span class="k">IS</span> <span class="k">NOT</span> <span class="k">NULL</span> |
| <span class="k">PRIMARY</span> <span class="k">KEY</span> <span class="p">(</span><span class="n">population</span><span class="p">,</span> <span class="n">species</span><span class="p">)</span> |
| <span class="k">WITH</span> <span class="n">comment</span><span class="o">=</span><span class="s1">'Allow query by population instead of species'</span><span class="p">;</span> |
| </pre></div> |
| </div> |
| <p>The <code class="docutils literal"><span class="pre">CREATE</span> <span class="pre">MATERIALIZED</span> <span class="pre">VIEW</span></code> statement creates a new materialized view. Each such view is a set of <em>rows</em> which |
| corresponds to rows which are present in the underlying, or base, table specified in the <code class="docutils literal"><span class="pre">SELECT</span></code> statement. A |
| materialized view cannot be directly updated, but updates to the base table will cause corresponding updates in the |
| view.</p> |
| <p>Creating a materialized view has 3 main parts:</p> |
| <ul class="simple"> |
| <li>The <a class="reference internal" href="#mv-select"><span class="std std-ref">select statement</span></a> that restrict the data included in the view.</li> |
| <li>The <a class="reference internal" href="#mv-primary-key"><span class="std std-ref">primary key</span></a> definition for the view.</li> |
| <li>The <a class="reference internal" href="#mv-options"><span class="std std-ref">options</span></a> for the view.</li> |
| </ul> |
| <p>Attempting to create an already existing materialized view will return an error unless the <code class="docutils literal"><span class="pre">IF</span> <span class="pre">NOT</span> <span class="pre">EXISTS</span></code> option is |
| used. If it is used, the statement will be a no-op if the materialized view already exists.</p> |
| <div class="section" id="mv-select-statement"> |
| <span id="mv-select"></span><h3>MV select statement<a class="headerlink" href="#mv-select-statement" title="Permalink to this headline">¶</a></h3> |
| <p>The select statement of a materialized view creation defines which of the base table is included in the view. That |
| statement is limited in a number of ways:</p> |
| <ul class="simple"> |
| <li>the <a class="reference internal" href="dml.html#selection-clause"><span class="std std-ref">selection</span></a> is limited to those that only select columns of the base table. In other |
| words, you can’t use any function (aggregate or not), casting, term, etc. Aliases are also not supported. You can |
| however use <cite>*</cite> as a shortcut of selecting all columns. Further, <a class="reference internal" href="ddl.html#static-columns"><span class="std std-ref">static columns</span></a> cannot be |
| included in a materialized view (which means <code class="docutils literal"><span class="pre">SELECT</span> <span class="pre">*</span></code> isn’t allowed if the base table has static columns).</li> |
| <li>the <code class="docutils literal"><span class="pre">WHERE</span></code> clause have the following restrictions:<ul> |
| <li>it cannot include any <a class="reference internal" href="definitions.html#grammar-token-bind_marker"><code class="xref std std-token docutils literal"><span class="pre">bind_marker</span></code></a>.</li> |
| <li>the columns that are not part of the <em>base table</em> primary key can only be restricted by an <code class="docutils literal"><span class="pre">IS</span> <span class="pre">NOT</span> <span class="pre">NULL</span></code> |
| restriction. No other restriction is allowed.</li> |
| <li>as the columns that are part of the <em>view</em> primary key cannot be null, they must always be at least restricted by a |
| <code class="docutils literal"><span class="pre">IS</span> <span class="pre">NOT</span> <span class="pre">NULL</span></code> restriction (or any other restriction, but they must have one).</li> |
| </ul> |
| </li> |
| <li>it cannot have neither an <a class="reference internal" href="dml.html#ordering-clause"><span class="std std-ref">ordering clause</span></a>, nor a <a class="reference internal" href="dml.html#limit-clause"><span class="std std-ref">limit</span></a>, nor <a class="reference internal" href="dml.html#allow-filtering"><span class="std std-ref">ALLOW |
| FILTERING</span></a>.</li> |
| </ul> |
| </div> |
| <div class="section" id="mv-primary-key"> |
| <span id="id2"></span><h3>MV primary key<a class="headerlink" href="#mv-primary-key" title="Permalink to this headline">¶</a></h3> |
| <p>A view must have a primary key and that primary key must conform to the following restrictions:</p> |
| <ul class="simple"> |
| <li>it must contain all the primary key columns of the base table. This ensures that every row of the view correspond to |
| exactly one row of the base table.</li> |
| <li>it can only contain a single column that is not a primary key column in the base table.</li> |
| </ul> |
| <p>So for instance, give the following base table definition:</p> |
| <div class="highlight-cql"><div class="highlight"><pre><span></span><span class="k">CREATE</span> <span class="k">TABLE</span> <span class="n">t</span> <span class="p">(</span> |
| <span class="n">k</span> <span class="nb">int</span><span class="p">,</span> |
| <span class="n">c1</span> <span class="nb">int</span><span class="p">,</span> |
| <span class="n">c2</span> <span class="nb">int</span><span class="p">,</span> |
| <span class="n">v1</span> <span class="nb">int</span><span class="p">,</span> |
| <span class="n">v2</span> <span class="nb">int</span><span class="p">,</span> |
| <span class="k">PRIMARY</span> <span class="k">KEY</span> <span class="p">(</span><span class="n">k</span><span class="p">,</span> <span class="n">c1</span><span class="p">,</span> <span class="n">c2</span><span class="p">)</span> |
| <span class="p">)</span> |
| </pre></div> |
| </div> |
| <p>then the following view definitions are allowed:</p> |
| <div class="highlight-cql"><div class="highlight"><pre><span></span><span class="k">CREATE</span> <span class="k">MATERIALIZED</span> <span class="k">VIEW</span> <span class="n">mv1</span> <span class="k">AS</span> |
| <span class="k">SELECT</span> <span class="o">*</span> <span class="k">FROM</span> <span class="n">t</span> <span class="k">WHERE</span> <span class="n">k</span> <span class="k">IS</span> <span class="k">NOT</span> <span class="k">NULL</span> <span class="k">AND</span> <span class="n">c1</span> <span class="k">IS</span> <span class="k">NOT</span> <span class="k">NULL</span> <span class="k">AND</span> <span class="n">c2</span> <span class="k">IS</span> <span class="k">NOT</span> <span class="k">NULL</span> |
| <span class="k">PRIMARY</span> <span class="k">KEY</span> <span class="p">(</span><span class="n">c1</span><span class="p">,</span> <span class="n">k</span><span class="p">,</span> <span class="n">c2</span><span class="p">)</span> |
| |
| <span class="k">CREATE</span> <span class="k">MATERIALIZED</span> <span class="k">VIEW</span> <span class="n">mv1</span> <span class="k">AS</span> |
| <span class="k">SELECT</span> <span class="o">*</span> <span class="k">FROM</span> <span class="n">t</span> <span class="k">WHERE</span> <span class="n">k</span> <span class="k">IS</span> <span class="k">NOT</span> <span class="k">NULL</span> <span class="k">AND</span> <span class="n">c1</span> <span class="k">IS</span> <span class="k">NOT</span> <span class="k">NULL</span> <span class="k">AND</span> <span class="n">c2</span> <span class="k">IS</span> <span class="k">NOT</span> <span class="k">NULL</span> |
| <span class="k">PRIMARY</span> <span class="k">KEY</span> <span class="p">(</span><span class="n">v1</span><span class="p">,</span> <span class="n">k</span><span class="p">,</span> <span class="n">c1</span><span class="p">,</span> <span class="n">c2</span><span class="p">)</span> |
| </pre></div> |
| </div> |
| <p>but the following ones are <strong>not</strong> allowed:</p> |
| <div class="highlight-cql"><div class="highlight"><pre><span></span><span class="c1">// Error: cannot include both v1 and v2 in the primary key as both are not in the base table primary key</span> |
| <span class="k">CREATE</span> <span class="k">MATERIALIZED</span> <span class="k">VIEW</span> <span class="n">mv1</span> <span class="k">AS</span> |
| <span class="k">SELECT</span> <span class="o">*</span> <span class="k">FROM</span> <span class="n">t</span> <span class="k">WHERE</span> <span class="n">k</span> <span class="k">IS</span> <span class="k">NOT</span> <span class="k">NULL</span> <span class="k">AND</span> <span class="n">c1</span> <span class="k">IS</span> <span class="k">NOT</span> <span class="k">NULL</span> <span class="k">AND</span> <span class="n">c2</span> <span class="k">IS</span> <span class="k">NOT</span> <span class="k">NULL</span> <span class="k">AND</span> <span class="n">v1</span> <span class="k">IS</span> <span class="k">NOT</span> <span class="k">NULL</span> |
| <span class="k">PRIMARY</span> <span class="k">KEY</span> <span class="p">(</span><span class="n">v1</span><span class="p">,</span> <span class="n">v2</span><span class="p">,</span> <span class="n">k</span><span class="p">,</span> <span class="n">c1</span><span class="p">,</span> <span class="n">c2</span><span class="p">)</span> |
| |
| <span class="c1">// Error: must include k in the primary as it's a base table primary key column</span> |
| <span class="k">CREATE</span> <span class="k">MATERIALIZED</span> <span class="k">VIEW</span> <span class="n">mv1</span> <span class="k">AS</span> |
| <span class="k">SELECT</span> <span class="o">*</span> <span class="k">FROM</span> <span class="n">t</span> <span class="k">WHERE</span> <span class="n">c1</span> <span class="k">IS</span> <span class="k">NOT</span> <span class="k">NULL</span> <span class="k">AND</span> <span class="n">c2</span> <span class="k">IS</span> <span class="k">NOT</span> <span class="k">NULL</span> |
| <span class="k">PRIMARY</span> <span class="k">KEY</span> <span class="p">(</span><span class="n">c1</span><span class="p">,</span> <span class="n">c2</span><span class="p">)</span> |
| </pre></div> |
| </div> |
| </div> |
| <div class="section" id="mv-options"> |
| <span id="id3"></span><h3>MV options<a class="headerlink" href="#mv-options" title="Permalink to this headline">¶</a></h3> |
| <p>A materialized view is internally implemented by a table and as such, creating a MV allows the <a class="reference internal" href="ddl.html#create-table-options"><span class="std std-ref">same options than |
| creating a table</span></a>.</p> |
| </div> |
| </div> |
| <div class="section" id="alter-materialized-view"> |
| <span id="alter-materialized-view-statement"></span><h2>ALTER MATERIALIZED VIEW<a class="headerlink" href="#alter-materialized-view" title="Permalink to this headline">¶</a></h2> |
| <p>After creation, you can alter the options of a materialized view using the <code class="docutils literal"><span class="pre">ALTER</span> <span class="pre">MATERIALIZED</span> <span class="pre">VIEW</span></code> statement:</p> |
| <pre> |
| <strong id="grammar-token-alter_materialized_view_statement">alter_materialized_view_statement</strong> ::= ALTER MATERIALIZED VIEW <a class="reference internal" href="#grammar-token-view_name"><code class="xref docutils literal"><span class="pre">view_name</span></code></a> WITH <a class="reference internal" href="ddl.html#grammar-token-table_options"><code class="xref docutils literal"><span class="pre">table_options</span></code></a> |
| </pre> |
| <p>The options that can be updated are the same than at creation time and thus the <a class="reference internal" href="ddl.html#create-table-options"><span class="std std-ref">same than for tables</span></a>.</p> |
| </div> |
| <div class="section" id="drop-materialized-view"> |
| <span id="drop-materialized-view-statement"></span><h2>DROP MATERIALIZED VIEW<a class="headerlink" href="#drop-materialized-view" title="Permalink to this headline">¶</a></h2> |
| <p>Dropping a materialized view users the <code class="docutils literal"><span class="pre">DROP</span> <span class="pre">MATERIALIZED</span> <span class="pre">VIEW</span></code> statement:</p> |
| <pre> |
| <strong id="grammar-token-drop_materialized_view_statement">drop_materialized_view_statement</strong> ::= DROP MATERIALIZED VIEW [ IF EXISTS ] <a class="reference internal" href="#grammar-token-view_name"><code class="xref docutils literal"><span class="pre">view_name</span></code></a>; |
| </pre> |
| <p>If the materialized view does not exists, the statement will return an error, unless <code class="docutils literal"><span class="pre">IF</span> <span class="pre">EXISTS</span></code> is used in which case |
| the operation is a no-op.</p> |
| </div> |
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