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Schema Definition Language
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SQLAlchemy 1.2 Documentation
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Release: <span class="version-num">1.2.19</span>
| Release Date: April 15, 2019
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<h1>SQLAlchemy 1.2 Documentation</h1>
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<h3><a href="../index.html">SQLAlchemy 1.2 Documentation</a></h3>
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<a href="index.html" title="SQLAlchemy Core">SQLAlchemy Core</a>
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<li><span class="link-container"><a class="reference external" href="tutorial.html">SQL Expression Language Tutorial</a></span></li>
<li><span class="link-container"><a class="reference external" href="expression_api.html">SQL Statements and Expressions API</a></span></li>
<li class="selected"><span class="link-container"><strong>Schema Definition Language</strong><a class="paramlink headerlink reference internal" href="#">¶</a></span><ul>
<li><span class="link-container"><a class="reference external" href="metadata.html">Describing Databases with MetaData</a></span></li>
<li><span class="link-container"><a class="reference external" href="reflection.html">Reflecting Database Objects</a></span></li>
<li><span class="link-container"><a class="reference external" href="defaults.html">Column Insert/Update Defaults</a></span></li>
<li><span class="link-container"><a class="reference external" href="constraints.html">Defining Constraints and Indexes</a></span></li>
<li><span class="link-container"><a class="reference external" href="ddl.html">Customizing DDL</a></span></li>
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<li><span class="link-container"><a class="reference external" href="types.html">Column and Data Types</a></span></li>
<li><span class="link-container"><a class="reference external" href="engines_connections.html">Engine and Connection Use</a></span></li>
<li><span class="link-container"><a class="reference external" href="api_basics.html">Core API Basics</a></span></li>
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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">¶</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"><code class="xref py py-class docutils literal notranslate"><span class="pre">Table</span></code></a>, <a class="reference internal" href="metadata.html#sqlalchemy.schema.Column" title="sqlalchemy.schema.Column"><code class="xref py py-class docutils literal notranslate"><span class="pre">Column</span></code></a>,
<a class="reference internal" href="constraints.html#sqlalchemy.schema.ForeignKey" title="sqlalchemy.schema.ForeignKey"><code class="xref py py-class docutils literal notranslate"><span class="pre">ForeignKey</span></code></a> and
<a class="reference internal" href="defaults.html#sqlalchemy.schema.Sequence" title="sqlalchemy.schema.Sequence"><code class="xref py py-class docutils literal notranslate"><span class="pre">Sequence</span></code></a>, all of which are imported from the
<code class="docutils literal notranslate"><span class="pre">sqlalchemy.schema</span></code> 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"><code class="xref py py-class docutils literal notranslate"><span class="pre">Table</span></code></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><ul>
<li class="toctree-l2"><a class="reference internal" href="metadata.html#accessing-tables-and-columns">Accessing Tables and Columns</a></li>
<li class="toctree-l2"><a class="reference internal" href="metadata.html#creating-and-dropping-database-tables">Creating and Dropping Database Tables</a></li>
<li class="toctree-l2"><a class="reference internal" href="metadata.html#altering-schemas-through-migrations">Altering Schemas through Migrations</a></li>
<li class="toctree-l2"><a class="reference internal" href="metadata.html#specifying-the-schema-name">Specifying the Schema Name</a></li>
<li class="toctree-l2"><a class="reference internal" href="metadata.html#backend-specific-options">Backend-Specific Options</a></li>
<li class="toctree-l2"><a class="reference internal" href="metadata.html#column-table-metadata-api">Column, Table, MetaData API</a></li>
</ul>
</li>
<li class="toctree-l1"><a class="reference internal" href="reflection.html">Reflecting Database Objects</a><ul>
<li class="toctree-l2"><a class="reference internal" href="reflection.html#overriding-reflected-columns">Overriding Reflected Columns</a></li>
<li class="toctree-l2"><a class="reference internal" href="reflection.html#reflecting-views">Reflecting Views</a></li>
<li class="toctree-l2"><a class="reference internal" href="reflection.html#reflecting-all-tables-at-once">Reflecting All Tables at Once</a></li>
<li class="toctree-l2"><a class="reference internal" href="reflection.html#fine-grained-reflection-with-inspector">Fine Grained Reflection with Inspector</a></li>
<li class="toctree-l2"><a class="reference internal" href="reflection.html#limitations-of-reflection">Limitations of Reflection</a></li>
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<li class="toctree-l1"><a class="reference internal" href="defaults.html">Column Insert/Update Defaults</a><ul>
<li class="toctree-l2"><a class="reference internal" href="defaults.html#scalar-defaults">Scalar Defaults</a></li>
<li class="toctree-l2"><a class="reference internal" href="defaults.html#python-executed-functions">Python-Executed Functions</a></li>
<li class="toctree-l2"><a class="reference internal" href="defaults.html#client-invoked-sql-expressions">Client-Invoked SQL Expressions</a></li>
<li class="toctree-l2"><a class="reference internal" href="defaults.html#server-invoked-ddl-explicit-default-expressions">Server-invoked DDL-Explicit Default Expressions</a></li>
<li class="toctree-l2"><a class="reference internal" href="defaults.html#marking-implicitly-generated-values-timestamps-and-triggered-columns">Marking Implicitly Generated Values, timestamps, and Triggered Columns</a></li>
<li class="toctree-l2"><a class="reference internal" href="defaults.html#defining-sequences">Defining Sequences</a></li>
<li class="toctree-l2"><a class="reference internal" href="defaults.html#default-objects-api">Default Objects API</a></li>
</ul>
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<li class="toctree-l1"><a class="reference internal" href="constraints.html">Defining Constraints and Indexes</a><ul>
<li class="toctree-l2"><a class="reference internal" href="constraints.html#defining-foreign-keys">Defining Foreign Keys</a></li>
<li class="toctree-l2"><a class="reference internal" href="constraints.html#unique-constraint">UNIQUE Constraint</a></li>
<li class="toctree-l2"><a class="reference internal" href="constraints.html#check-constraint">CHECK Constraint</a></li>
<li class="toctree-l2"><a class="reference internal" href="constraints.html#primary-key-constraint">PRIMARY KEY Constraint</a></li>
<li class="toctree-l2"><a class="reference internal" href="constraints.html#setting-up-constraints-when-using-the-declarative-orm-extension">Setting up Constraints when using the Declarative ORM Extension</a></li>
<li class="toctree-l2"><a class="reference internal" href="constraints.html#configuring-constraint-naming-conventions">Configuring Constraint Naming Conventions</a></li>
<li class="toctree-l2"><a class="reference internal" href="constraints.html#constraints-api">Constraints API</a></li>
<li class="toctree-l2"><a class="reference internal" href="constraints.html#indexes">Indexes</a></li>
<li class="toctree-l2"><a class="reference internal" href="constraints.html#index-api">Index API</a></li>
</ul>
</li>
<li class="toctree-l1"><a class="reference internal" href="ddl.html">Customizing DDL</a><ul>
<li class="toctree-l2"><a class="reference internal" href="ddl.html#custom-ddl">Custom DDL</a></li>
<li class="toctree-l2"><a class="reference internal" href="ddl.html#controlling-ddl-sequences">Controlling DDL Sequences</a></li>
<li class="toctree-l2"><a class="reference internal" href="ddl.html#using-the-built-in-ddlelement-classes">Using the built-in DDLElement Classes</a></li>
<li class="toctree-l2"><a class="reference internal" href="ddl.html#ddl-expression-constructs-api">DDL Expression Constructs API</a></li>
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