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Schema Definition Language
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SQLAlchemy 0.8 Documentation
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Release: <span class="version-num">0.8.7</span> | Release Date: July 22, 2014
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<h1>SQLAlchemy 0.8 Documentation</h1>
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<h3><a href="../index.html">SQLAlchemy 0.8 Documentation</a></h3>
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Schema Definition Language
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<li><a class="reference internal" href="#">Schema Definition Language</a><ul>
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<div class="section" id="module-sqlalchemy.schema">
<span id="schema-definition-language"></span><span id="schema-toplevel"></span><h1>Schema Definition Language<a class="headerlink" href="#module-sqlalchemy.schema" title="Permalink to this headline">ΒΆ</a></h1>
<p>This section references SQLAlchemy <strong>schema metadata</strong>, a comprehensive system of describing and inspecting
database schemas.</p>
<p>The core of SQLAlchemy’s query and object mapping operations are supported by
<em>database metadata</em>, which is comprised of Python objects that describe tables
and other schema-level objects. These objects are at the core of three major
types of operations - issuing CREATE and DROP statements (known as <em>DDL</em>),
constructing SQL queries, and expressing information about structures that
already exist within the database.</p>
<p>Database metadata can be expressed by explicitly naming the various components
and their properties, using constructs such as
<a class="reference internal" href="metadata.html#sqlalchemy.schema.Table" title="sqlalchemy.schema.Table"><tt class="xref py py-class docutils literal"><span class="pre">Table</span></tt></a>, <a class="reference internal" href="metadata.html#sqlalchemy.schema.Column" title="sqlalchemy.schema.Column"><tt class="xref py py-class docutils literal"><span class="pre">Column</span></tt></a>,
<a class="reference internal" href="constraints.html#sqlalchemy.schema.ForeignKey" title="sqlalchemy.schema.ForeignKey"><tt class="xref py py-class docutils literal"><span class="pre">ForeignKey</span></tt></a> and
<a class="reference internal" href="defaults.html#sqlalchemy.schema.Sequence" title="sqlalchemy.schema.Sequence"><tt class="xref py py-class docutils literal"><span class="pre">Sequence</span></tt></a>, all of which are imported from the
<tt class="docutils literal"><span class="pre">sqlalchemy.schema</span></tt> package. It can also be generated by SQLAlchemy using a
process called <em>reflection</em>, which means you start with a single object such
as <a class="reference internal" href="metadata.html#sqlalchemy.schema.Table" title="sqlalchemy.schema.Table"><tt class="xref py py-class docutils literal"><span class="pre">Table</span></tt></a>, assign it a name, and then instruct
SQLAlchemy to load all the additional information related to that name from a
particular engine source.</p>
<p>A key feature of SQLAlchemy’s database metadata constructs is that they are
designed to be used in a <em>declarative</em> style which closely resembles that of
real DDL. They are therefore most intuitive to those who have some background
in creating real schema generation scripts.</p>
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<li class="toctree-l1"><a class="reference internal" href="metadata.html">Describing Databases with MetaData</a></li>
<li class="toctree-l1"><a class="reference internal" href="reflection.html">Reflecting Database Objects</a></li>
<li class="toctree-l1"><a class="reference internal" href="defaults.html">Column Insert/Update Defaults</a></li>
<li class="toctree-l1"><a class="reference internal" href="constraints.html">Defining Constraints and Indexes</a></li>
<li class="toctree-l1"><a class="reference internal" href="ddl.html">Customizing DDL</a></li>
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