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| <h1 title="Package org.apache.calcite.sql.validate.implicit" class="title">Package org.apache.calcite.sql.validate.implicit</h1> |
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| <hr> |
| <div class="package-signature">package <span class="element-name">org.apache.calcite.sql.validate.implicit</span></div> |
| <section class="package-description" id="package-description"> |
| <div class="block"><h2>SQL Implicit Type Cast</h2> |
| |
| <h3>Work Flow</h3> |
| |
| <p>This package contains rules for implicit type coercion, it works during |
| the process of SQL validation. The transformation entrance are all kinds of |
| checkers. i.e. |
| <a href="../../type/AssignableOperandTypeChecker.html" title="class in org.apache.calcite.sql.type"><code>AssignableOperandTypeChecker</code></a>, |
| <a href="../../type/ComparableOperandTypeChecker.html" title="class in org.apache.calcite.sql.type"><code>ComparableOperandTypeChecker</code></a> |
| <a href="../../type/CompositeOperandTypeChecker.html" title="class in org.apache.calcite.sql.type"><code>CompositeOperandTypeChecker</code></a>, |
| <a href="../../type/FamilyOperandTypeChecker.html" title="class in org.apache.calcite.sql.type"><code>FamilyOperandTypeChecker</code></a>, |
| <a href="../../type/SameOperandTypeChecker.html" title="class in org.apache.calcite.sql.type"><code>SameOperandTypeChecker</code></a>, |
| <a href="../../type/SetopOperandTypeChecker.html" title="class in org.apache.calcite.sql.type"><code>SetopOperandTypeChecker</code></a>. |
| |
| <ul> |
| <li> |
| When user do validation for a <a href="../../SqlNode.html" title="class in org.apache.calcite.sql"><code>SqlNode</code></a>, |
| and the type coercion is turned on(default), the validator will check the |
| operands/return types of all kinds of operators, if the validation passes through, |
| the validator will just cache the data type (say RelDataType) for the |
| <a href="../../SqlNode.html" title="class in org.apache.calcite.sql"><code>SqlNode</code></a> it has validated;</li> |
| <li>If the validation fails, the validator will ask the |
| <a href="TypeCoercion.html" title="interface in org.apache.calcite.sql.validate.implicit"><code>TypeCoercion</code></a> about |
| if there can make implicit type coercion, if the coercion rules passed, the |
| <a href="TypeCoercion.html" title="interface in org.apache.calcite.sql.validate.implicit"><code>TypeCoercion</code></a> component |
| will replace the <a href="../../SqlNode.html" title="class in org.apache.calcite.sql"><code>SqlNode</code></a> with a casted one, |
| (the node may be an operand of an operator or a column field of a selected row).</li> |
| <li><a href="TypeCoercion.html" title="interface in org.apache.calcite.sql.validate.implicit"><code>TypeCoercion</code></a> |
| will then update the inferred type for the casted node and |
| the containing operator/row column type.</li> |
| <li>If the coercion rule fails again, the validator will just throw |
| the exception as is before.</li> |
| </ul> |
| |
| <p>For some cases, although the validation passes, we still need the type coercion, e.g. for |
| expression 1 > '1', Calcite will just return false without type coercion, we do type coercion |
| eagerly here: the result expression would be transformed to "1 > cast('1' as int)" and |
| the result would be true. |
| |
| <h3>Conversion SQL Contexts</h3> |
| |
| <p>The supported conversion contexts are: |
| <a href="https://docs.google.com/document/d/1g2RUnLXyp_LjUlO-wbblKuP5hqEu3a_2Mt2k4dh6RwU/edit?usp=sharing">Conversion Expressions</a> |
| |
| <p>Strategies for Finding Common Type:</p> |
| <ul> |
| <li>If the operator has expected data types, just take them as the desired one. i.e. the UDF. |
| </li> |
| <li>If there is no expected data type but data type families are registered, try to coerce |
| operand to the family's default data type, i.e. the STRING family will have a VARCHAR type. |
| </li> |
| <li>If neither expected data type nor families are specified, try to find the tightest common |
| type of the node types, i.e. INTEGER and DOUBLE will return DOUBLE, the numeric precision |
| does not lose for this case.</li> |
| <li>If no tightest common type is found, try to find a wider type, i.e. STRING and INT |
| will return int, we allow some precision loss when widening DECIMAL to fractional, |
| or promote to STRING.</li> |
| </ul> |
| |
| <h3>Type Conversion Matrix</h3> |
| |
| <p>See <a href="https://docs.google.com/spreadsheets/d/1GhleX5h5W8-kJKh7NMJ4vtoE78pwfaZRJl88ULX_MgU/edit?usp=sharing">CalciteImplicitCasts</a>.</div> |
| </section> |
| <section class="summary"> |
| <ul class="summary-list"> |
| <li> |
| <div id="related-package-summary"> |
| <div class="caption"><span>Related Packages</span></div> |
| <div class="summary-table two-column-summary"> |
| <div class="table-header col-first">Package</div> |
| <div class="table-header col-last">Description</div> |
| <div class="col-first even-row-color"><a href="../package-summary.html">org.apache.calcite.sql.validate</a></div> |
| <div class="col-last even-row-color"> |
| <div class="block">SQL validation.</div> |
| </div> |
| </div> |
| </div> |
| </li> |
| <li> |
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| <div class="table-tabs" role="tablist" aria-orientation="horizontal"><button id="class-summary-tab0" role="tab" aria-selected="true" aria-controls="class-summary.tabpanel" tabindex="0" onkeydown="switchTab(event)" onclick="show('class-summary', 'class-summary', 2)" class="active-table-tab">All Classes and Interfaces</button><button id="class-summary-tab1" role="tab" aria-selected="false" aria-controls="class-summary.tabpanel" tabindex="-1" onkeydown="switchTab(event)" onclick="show('class-summary', 'class-summary-tab1', 2)" class="table-tab">Interfaces</button><button id="class-summary-tab2" role="tab" aria-selected="false" aria-controls="class-summary.tabpanel" tabindex="-1" onkeydown="switchTab(event)" onclick="show('class-summary', 'class-summary-tab2', 2)" class="table-tab">Classes</button></div> |
| <div id="class-summary.tabpanel" role="tabpanel"> |
| <div class="summary-table two-column-summary" aria-labelledby="class-summary-tab0"> |
| <div class="table-header col-first">Class</div> |
| <div class="table-header col-last">Description</div> |
| <div class="col-first even-row-color class-summary class-summary-tab2"><a href="AbstractTypeCoercion.html" title="class in org.apache.calcite.sql.validate.implicit">AbstractTypeCoercion</a></div> |
| <div class="col-last even-row-color class-summary class-summary-tab2"> |
| <div class="block">Base class for all the type coercion rules.</div> |
| </div> |
| <div class="col-first odd-row-color class-summary class-summary-tab1"><a href="TypeCoercion.html" title="interface in org.apache.calcite.sql.validate.implicit">TypeCoercion</a></div> |
| <div class="col-last odd-row-color class-summary class-summary-tab1"> |
| <div class="block">Default strategies to coerce differing types that participate in |
| operations into compatible ones.</div> |
| </div> |
| <div class="col-first even-row-color class-summary class-summary-tab1"><a href="TypeCoercionFactory.html" title="interface in org.apache.calcite.sql.validate.implicit">TypeCoercionFactory</a></div> |
| <div class="col-last even-row-color class-summary class-summary-tab1"> |
| <div class="block">Factory for <a href="TypeCoercion.html" title="interface in org.apache.calcite.sql.validate.implicit"><code>TypeCoercion</code></a> objects.</div> |
| </div> |
| <div class="col-first odd-row-color class-summary class-summary-tab2"><a href="TypeCoercionImpl.html" title="class in org.apache.calcite.sql.validate.implicit">TypeCoercionImpl</a></div> |
| <div class="col-last odd-row-color class-summary class-summary-tab2"> |
| <div class="block">Default implementation of Calcite implicit type cast.</div> |
| </div> |
| <div class="col-first even-row-color class-summary class-summary-tab2"><a href="TypeCoercions.html" title="class in org.apache.calcite.sql.validate.implicit">TypeCoercions</a></div> |
| <div class="col-last even-row-color class-summary class-summary-tab2"> |
| <div class="block">Factory class for type coercion instantiation of different sql dialects.</div> |
| </div> |
| </div> |
| </div> |
| </div> |
| </li> |
| </ul> |
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