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| <h1 title="程序包" class="title">程序包 org.apache.calcite.sql.validate.implicit</h1> |
| <div class="docSummary"> |
| <div class="block">SQL Implicit Type Cast |
| |
| Work Flow |
| |
| This package contains rules for implicit type coercion, it works during |
| the process of SQL validation.</div> |
| </div> |
| <p>请参阅: <a href="#package.description">说明</a></p> |
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| <tr> |
| <th class="colFirst" scope="col">接口</th> |
| <th class="colLast" scope="col">说明</th> |
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| <tbody> |
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| <td class="colFirst"><a href="../../../../../../org/apache/calcite/sql/validate/implicit/TypeCoercion.html" title="org.apache.calcite.sql.validate.implicit中的接口">TypeCoercion</a></td> |
| <td class="colLast"> |
| <div class="block">Default strategies to coerce differing types that participate in |
| operations into compatible ones.</div> |
| </td> |
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| <td class="colFirst"><a href="../../../../../../org/apache/calcite/sql/validate/implicit/AbstractTypeCoercion.html" title="org.apache.calcite.sql.validate.implicit中的类">AbstractTypeCoercion</a></td> |
| <td class="colLast"> |
| <div class="block">Base class for all the type coercion rules.</div> |
| </td> |
| </tr> |
| <tr class="rowColor"> |
| <td class="colFirst"><a href="../../../../../../org/apache/calcite/sql/validate/implicit/TypeCoercionImpl.html" title="org.apache.calcite.sql.validate.implicit中的类">TypeCoercionImpl</a></td> |
| <td class="colLast"> |
| <div class="block">Default implementation of Calcite implicit type cast.</div> |
| </td> |
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| <td class="colFirst"><a href="../../../../../../org/apache/calcite/sql/validate/implicit/TypeCoercions.html" title="org.apache.calcite.sql.validate.implicit中的类">TypeCoercions</a></td> |
| <td class="colLast"> |
| <div class="block">Factory class for type coercion instantiation of different sql dialects.</div> |
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| <h2 title="程序包org.apache.calcite.sql.validate.implicit的说明">程序包org.apache.calcite.sql.validate.implicit的说明</h2> |
| <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="../../../../../../org/apache/calcite/sql/type/AssignableOperandTypeChecker.html" title="org.apache.calcite.sql.type中的类"><code>AssignableOperandTypeChecker</code></a>, |
| <a href="../../../../../../org/apache/calcite/sql/type/ComparableOperandTypeChecker.html" title="org.apache.calcite.sql.type中的类"><code>ComparableOperandTypeChecker</code></a> |
| <a href="../../../../../../org/apache/calcite/sql/type/CompositeOperandTypeChecker.html" title="org.apache.calcite.sql.type中的类"><code>CompositeOperandTypeChecker</code></a>, |
| <a href="../../../../../../org/apache/calcite/sql/type/FamilyOperandTypeChecker.html" title="org.apache.calcite.sql.type中的类"><code>FamilyOperandTypeChecker</code></a>, |
| <a href="../../../../../../org/apache/calcite/sql/type/SameOperandTypeChecker.html" title="org.apache.calcite.sql.type中的类"><code>SameOperandTypeChecker</code></a>, |
| <a href="../../../../../../org/apache/calcite/sql/type/SetopOperandTypeChecker.html" title="org.apache.calcite.sql.type中的类"><code>SetopOperandTypeChecker</code></a>. |
| |
| <ul> |
| <li> |
| When user do validation for a <a href="../../../../../../org/apache/calcite/sql/SqlNode.html" title="org.apache.calcite.sql中的类"><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="../../../../../../org/apache/calcite/sql/SqlNode.html" title="org.apache.calcite.sql中的类"><code>SqlNode</code></a> it has validated;</li> |
| <li>If the validation fails, the validator will ask the |
| <a href="../../../../../../org/apache/calcite/sql/validate/implicit/TypeCoercion.html" title="org.apache.calcite.sql.validate.implicit中的接口"><code>TypeCoercion</code></a> about |
| if there can make implicit type coercion, if the coercion rules passed, the |
| <a href="../../../../../../org/apache/calcite/sql/validate/implicit/TypeCoercion.html" title="org.apache.calcite.sql.validate.implicit中的接口"><code>TypeCoercion</code></a> component |
| will replace the <a href="../../../../../../org/apache/calcite/sql/SqlNode.html" title="org.apache.calcite.sql中的类"><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="../../../../../../org/apache/calcite/sql/validate/implicit/TypeCoercion.html" title="org.apache.calcite.sql.validate.implicit中的接口"><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> |
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