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| <div class="subTitle">org.apache.drill.exec.physical.impl.scan.v3</div> |
| <h2 title="Interface SchemaNegotiator" class="title">Interface SchemaNegotiator</h2> |
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| <dt>All Known Subinterfaces:</dt> |
| <dd><a href="../../../../../../../../org/apache/drill/exec/physical/impl/scan/v3/file/FileSchemaNegotiator.html" title="interface in org.apache.drill.exec.physical.impl.scan.v3.file">FileSchemaNegotiator</a></dd> |
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| <dt>All Known Implementing Classes:</dt> |
| <dd><a href="../../../../../../../../org/apache/drill/exec/physical/impl/scan/v3/file/FileSchemaNegotiatorImpl.html" title="class in org.apache.drill.exec.physical.impl.scan.v3.file">FileSchemaNegotiatorImpl</a>, <a href="../../../../../../../../org/apache/drill/exec/physical/impl/scan/v3/lifecycle/SchemaNegotiatorImpl.html" title="class in org.apache.drill.exec.physical.impl.scan.v3.lifecycle">SchemaNegotiatorImpl</a></dd> |
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| <br> |
| <pre>public interface <span class="typeNameLabel">SchemaNegotiator</span></pre> |
| <div class="block">Negotiates the table schema with the scanner framework and provides |
| context information for the reader. Scans use either a "dynamic" or |
| a defined schema. |
| <p> |
| Regardless of the schema type, the result of building the schema is a |
| result set loader used to prepare batches for use in the query. The reader |
| can simply read all columns, allowing the framework to discard unwanted |
| values. Or for efficiency, the reader can check the column metadata to |
| determine if a column is projected, and if not, then don't even read |
| the column from the input source. |
| |
| <h4>Defined Schema</h4> |
| |
| If defined, the execution plan provides the output schema (presumably |
| computed from an accurate metadata source.) The reader must populate |
| the proscribed rows, performing column type conversions as needed. |
| The reader can determine if the schema is defined by calling |
| <code>hasOutputSchema()</code>. |
| <p> |
| At present, the scan framework filters the "provided schema" against |
| the project list so that this class presents only the actual output |
| schema. Future versions may do the filtering in the planner, but |
| the result for readers will be the same either way. |
| |
| <h4>Dynamic Schema</h4> |
| |
| A dynamic schema occurs when the plan does not specify a schema. |
| Drill is unique in its support for "schema on read" in the sense |
| that Drill does not know the schema until the reader defines it at |
| scan time. |
| <p> |
| The reader and scan framework coordinate to form the output schema. |
| The reader offers the columns it has available. The scan framework |
| uses the projection list to decide which to accept. Either way the |
| scan framework provides a column reader for the column (returning a |
| do-nothing "dummy" reader if the column is unprojected.) |
| <p> |
| With a dynamic schema, readers offer a schema in one of two ways: |
| <p> |
| The reader provides the table schema in one of two ways: early schema |
| or late schema. Either way, the project list from the physical plan |
| determines which |
| table columns are materialized and which are not. Readers are provided |
| for all table columns for readers that must read sequentially, but |
| only the materialized columns are written to value vectors. |
| |
| <h4>Early Dynamic Schema</h4> |
| |
| Some readers can determine the source schema at the start of a scan. |
| For example, a CSV file has headers, a Parquet file has footers, both |
| of which define a schema. This case is called "early schema." The |
| reader fefines the schema by calling |
| <a href="../../../../../../../../org/apache/drill/exec/physical/impl/scan/v3/SchemaNegotiator.html#tableSchema-org.apache.drill.exec.record.metadata.TupleMetadata-"><code>tableSchema(TupleMetadata)</code></a> to provide the known schema. |
| |
| <h4>Late Dynamic Schema</h4> |
| |
| Other readers don't know the input schema until the reader actually |
| reads the data. For example, JSON typically has no schema, but does |
| have sufficient structure (name/value pairs) to infer one. |
| <p> |
| The late schema reader calls <code>RowSetLoader#addColumn()</code> to |
| add each column as it is discovered during the scan. |
| <p> |
| Note that, to avoid schema conflicts, a late schema reader |
| <i><b>must</b></i> define the full set of columns in the first batch, |
| and must stick to that schema for all subsequent batches. This allows |
| the reader to look one batch ahead to learn the columns. |
| <p> |
| Drill, however, cannot predict the future. Without a defined schema, |
| downstream operators cannot know which columns might appear later |
| in the scan, with which types. Today this is a strong guideline. |
| Future versions may enforce this rule.</div> |
| </li> |
| </ul> |
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| <div class="summary"> |
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| <!-- ========== METHOD SUMMARY =========== --> |
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| <h3>Method Summary</h3> |
| <table class="memberSummary" border="0" cellpadding="3" cellspacing="0" summary="Method Summary table, listing methods, and an explanation"> |
| <caption><span id="t0" class="activeTableTab"><span>All Methods</span><span class="tabEnd"> </span></span><span id="t2" class="tableTab"><span><a href="javascript:show(2);">Instance Methods</a></span><span class="tabEnd"> </span></span><span id="t3" class="tableTab"><span><a href="javascript:show(4);">Abstract Methods</a></span><span class="tabEnd"> </span></span></caption> |
| <tr> |
| <th class="colFirst" scope="col">Modifier and Type</th> |
| <th class="colLast" scope="col">Method and Description</th> |
| </tr> |
| <tr id="i0" class="altColor"> |
| <td class="colFirst"><code>void</code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../../../../../org/apache/drill/exec/physical/impl/scan/v3/SchemaNegotiator.html#batchSize-int-">batchSize</a></span>(int maxRecordsPerBatch)</code> |
| <div class="block">Set the preferred batch size (which may be overridden by the |
| result set loader in order to limit vector or batch size.)</div> |
| </td> |
| </tr> |
| <tr id="i1" class="rowColor"> |
| <td class="colFirst"><code><a href="../../../../../../../../org/apache/drill/exec/physical/resultSet/ResultSetLoader.html" title="interface in org.apache.drill.exec.physical.resultSet">ResultSetLoader</a></code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../../../../../org/apache/drill/exec/physical/impl/scan/v3/SchemaNegotiator.html#build--">build</a></span>()</code> |
| <div class="block">Build the schema, plan the required projections and static |
| columns and return a loader used to populate value vectors.</div> |
| </td> |
| </tr> |
| <tr id="i2" class="altColor"> |
| <td class="colFirst"><code><a href="../../../../../../../../org/apache/drill/exec/ops/OperatorContext.html" title="interface in org.apache.drill.exec.ops">OperatorContext</a></code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../../../../../org/apache/drill/exec/physical/impl/scan/v3/SchemaNegotiator.html#context--">context</a></span>()</code> </td> |
| </tr> |
| <tr id="i3" class="rowColor"> |
| <td class="colFirst"><code><a href="../../../../../../../../org/apache/drill/common/exceptions/CustomErrorContext.html" title="interface in org.apache.drill.common.exceptions">CustomErrorContext</a></code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../../../../../org/apache/drill/exec/physical/impl/scan/v3/SchemaNegotiator.html#errorContext--">errorContext</a></span>()</code> |
| <div class="block">Returns the error context to use for this reader: either the |
| parent or the reader-specific context set in |
| <a href="../../../../../../../../org/apache/drill/exec/physical/impl/scan/v3/SchemaNegotiator.html#setErrorContext-org.apache.drill.common.exceptions.CustomErrorContext-"><code>setErrorContext(CustomErrorContext)</code></a>.</div> |
| </td> |
| </tr> |
| <tr id="i4" class="altColor"> |
| <td class="colFirst"><code><a href="../../../../../../../../org/apache/drill/exec/record/metadata/TupleMetadata.html" title="interface in org.apache.drill.exec.record.metadata">TupleMetadata</a></code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../../../../../org/apache/drill/exec/physical/impl/scan/v3/SchemaNegotiator.html#inputSchema--">inputSchema</a></span>()</code> |
| <div class="block">Returns the reader input schema: the schema which describes the |
| set of columns this reader should produce.</div> |
| </td> |
| </tr> |
| <tr id="i5" class="rowColor"> |
| <td class="colFirst"><code>boolean</code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../../../../../org/apache/drill/exec/physical/impl/scan/v3/SchemaNegotiator.html#isProjectionEmpty--">isProjectionEmpty</a></span>()</code> |
| <div class="block">Report whether the projection list is empty, as occurs in two |
| cases: |
| |
| <tt>SELECT COUNT(*) ...</tt> -- empty project. |
| <tt>SELECT a, b FROM table(c d)</tt> -- disjoint project. |
| </div> |
| </td> |
| </tr> |
| <tr id="i6" class="altColor"> |
| <td class="colFirst"><code><a href="../../../../../../../../org/apache/drill/common/exceptions/CustomErrorContext.html" title="interface in org.apache.drill.common.exceptions">CustomErrorContext</a></code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../../../../../org/apache/drill/exec/physical/impl/scan/v3/SchemaNegotiator.html#parentErrorContext--">parentErrorContext</a></span>()</code> |
| <div class="block">The context to use as a parent when creating a custom context.</div> |
| </td> |
| </tr> |
| <tr id="i7" class="rowColor"> |
| <td class="colFirst"><code><a href="../../../../../../../../org/apache/drill/exec/physical/impl/scan/v3/schema/ProjectedColumn.html" title="class in org.apache.drill.exec.physical.impl.scan.v3.schema">ProjectedColumn</a></code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../../../../../org/apache/drill/exec/physical/impl/scan/v3/SchemaNegotiator.html#projectionFor-java.lang.String-">projectionFor</a></span>(<a href="https://docs.oracle.com/javase/8/docs/api/java/lang/String.html?is-external=true" title="class or interface in java.lang">String</a> colName)</code> </td> |
| </tr> |
| <tr id="i8" class="altColor"> |
| <td class="colFirst"><code><a href="../../../../../../../../org/apache/drill/exec/record/metadata/TupleMetadata.html" title="interface in org.apache.drill.exec.record.metadata">TupleMetadata</a></code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../../../../../org/apache/drill/exec/physical/impl/scan/v3/SchemaNegotiator.html#providedSchema--">providedSchema</a></span>()</code> |
| <div class="block">Returns the provided schema, if defined.</div> |
| </td> |
| </tr> |
| <tr id="i9" class="rowColor"> |
| <td class="colFirst"><code>void</code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../../../../../org/apache/drill/exec/physical/impl/scan/v3/SchemaNegotiator.html#schemaIsComplete-boolean-">schemaIsComplete</a></span>(boolean isComplete)</code> </td> |
| </tr> |
| <tr id="i10" class="altColor"> |
| <td class="colFirst"><code>void</code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../../../../../org/apache/drill/exec/physical/impl/scan/v3/SchemaNegotiator.html#setErrorContext-org.apache.drill.common.exceptions.CustomErrorContext-">setErrorContext</a></span>(<a href="../../../../../../../../org/apache/drill/common/exceptions/CustomErrorContext.html" title="interface in org.apache.drill.common.exceptions">CustomErrorContext</a> context)</code> |
| <div class="block">Specify an advanced error context which allows the reader to |
| fill in custom context values.</div> |
| </td> |
| </tr> |
| <tr id="i11" class="rowColor"> |
| <td class="colFirst"><code>void</code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../../../../../org/apache/drill/exec/physical/impl/scan/v3/SchemaNegotiator.html#tableSchema-org.apache.drill.exec.record.metadata.TupleMetadata-">tableSchema</a></span>(<a href="../../../../../../../../org/apache/drill/exec/record/metadata/TupleMetadata.html" title="interface in org.apache.drill.exec.record.metadata">TupleMetadata</a> schema)</code> </td> |
| </tr> |
| <tr id="i12" class="altColor"> |
| <td class="colFirst"><code>void</code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../../../../../org/apache/drill/exec/physical/impl/scan/v3/SchemaNegotiator.html#tableSchema-org.apache.drill.exec.record.metadata.TupleMetadata-boolean-">tableSchema</a></span>(<a href="../../../../../../../../org/apache/drill/exec/record/metadata/TupleMetadata.html" title="interface in org.apache.drill.exec.record.metadata">TupleMetadata</a> schema, |
| boolean isComplete)</code> |
| <div class="block">Specify the table schema if this is an early-schema reader.</div> |
| </td> |
| </tr> |
| <tr id="i13" class="rowColor"> |
| <td class="colFirst"><code><a href="https://docs.oracle.com/javase/8/docs/api/java/lang/String.html?is-external=true" title="class or interface in java.lang">String</a></code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../../../../../org/apache/drill/exec/physical/impl/scan/v3/SchemaNegotiator.html#userName--">userName</a></span>()</code> |
| <div class="block">Name of the user running the query.</div> |
| </td> |
| </tr> |
| </table> |
| </li> |
| </ul> |
| </li> |
| </ul> |
| </div> |
| <div class="details"> |
| <ul class="blockList"> |
| <li class="blockList"> |
| <!-- ============ METHOD DETAIL ========== --> |
| <ul class="blockList"> |
| <li class="blockList"><a name="method.detail"> |
| <!-- --> |
| </a> |
| <h3>Method Detail</h3> |
| <a name="context--"> |
| <!-- --> |
| </a> |
| <ul class="blockList"> |
| <li class="blockList"> |
| <h4>context</h4> |
| <pre><a href="../../../../../../../../org/apache/drill/exec/ops/OperatorContext.html" title="interface in org.apache.drill.exec.ops">OperatorContext</a> context()</pre> |
| </li> |
| </ul> |
| <a name="parentErrorContext--"> |
| <!-- --> |
| </a> |
| <ul class="blockList"> |
| <li class="blockList"> |
| <h4>parentErrorContext</h4> |
| <pre><a href="../../../../../../../../org/apache/drill/common/exceptions/CustomErrorContext.html" title="interface in org.apache.drill.common.exceptions">CustomErrorContext</a> parentErrorContext()</pre> |
| <div class="block">The context to use as a parent when creating a custom context. |
| <p> |
| (Obtain the error context for this reader from the |
| <a href="../../../../../../../../org/apache/drill/exec/physical/resultSet/ResultSetLoader.html" title="interface in org.apache.drill.exec.physical.resultSet"><code>ResultSetLoader</code></a>.</div> |
| </li> |
| </ul> |
| <a name="setErrorContext-org.apache.drill.common.exceptions.CustomErrorContext-"> |
| <!-- --> |
| </a> |
| <ul class="blockList"> |
| <li class="blockList"> |
| <h4>setErrorContext</h4> |
| <pre>void setErrorContext(<a href="../../../../../../../../org/apache/drill/common/exceptions/CustomErrorContext.html" title="interface in org.apache.drill.common.exceptions">CustomErrorContext</a> context)</pre> |
| <div class="block">Specify an advanced error context which allows the reader to |
| fill in custom context values.</div> |
| </li> |
| </ul> |
| <a name="errorContext--"> |
| <!-- --> |
| </a> |
| <ul class="blockList"> |
| <li class="blockList"> |
| <h4>errorContext</h4> |
| <pre><a href="../../../../../../../../org/apache/drill/common/exceptions/CustomErrorContext.html" title="interface in org.apache.drill.common.exceptions">CustomErrorContext</a> errorContext()</pre> |
| <div class="block">Returns the error context to use for this reader: either the |
| parent or the reader-specific context set in |
| <a href="../../../../../../../../org/apache/drill/exec/physical/impl/scan/v3/SchemaNegotiator.html#setErrorContext-org.apache.drill.common.exceptions.CustomErrorContext-"><code>setErrorContext(CustomErrorContext)</code></a>.</div> |
| </li> |
| </ul> |
| <a name="userName--"> |
| <!-- --> |
| </a> |
| <ul class="blockList"> |
| <li class="blockList"> |
| <h4>userName</h4> |
| <pre><a href="https://docs.oracle.com/javase/8/docs/api/java/lang/String.html?is-external=true" title="class or interface in java.lang">String</a> userName()</pre> |
| <div class="block">Name of the user running the query.</div> |
| </li> |
| </ul> |
| <a name="isProjectionEmpty--"> |
| <!-- --> |
| </a> |
| <ul class="blockList"> |
| <li class="blockList"> |
| <h4>isProjectionEmpty</h4> |
| <pre>boolean isProjectionEmpty()</pre> |
| <div class="block">Report whether the projection list is empty, as occurs in two |
| cases: |
| <ul> |
| <li><tt>SELECT COUNT(*) ...</tt> -- empty project.</ul> |
| <li><tt>SELECT a, b FROM table(c d)</tt> -- disjoint project.</li> |
| </ul></div> |
| <dl> |
| <dt><span class="returnLabel">Returns:</span></dt> |
| <dd>true if no columns are projected, and the client can |
| make use of <a href="../../../../../../../../org/apache/drill/exec/physical/resultSet/ResultSetLoader.html#skipRows-int-"><code>ResultSetLoader.skipRows(int)</code></a> to indicate the |
| row count, false if at least one column is projected and so |
| data must be written using the loader</dd> |
| </dl> |
| </li> |
| </ul> |
| <a name="projectionFor-java.lang.String-"> |
| <!-- --> |
| </a> |
| <ul class="blockList"> |
| <li class="blockList"> |
| <h4>projectionFor</h4> |
| <pre><a href="../../../../../../../../org/apache/drill/exec/physical/impl/scan/v3/schema/ProjectedColumn.html" title="class in org.apache.drill.exec.physical.impl.scan.v3.schema">ProjectedColumn</a> projectionFor(<a href="https://docs.oracle.com/javase/8/docs/api/java/lang/String.html?is-external=true" title="class or interface in java.lang">String</a> colName)</pre> |
| </li> |
| </ul> |
| <a name="providedSchema--"> |
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| </a> |
| <ul class="blockList"> |
| <li class="blockList"> |
| <h4>providedSchema</h4> |
| <pre><a href="../../../../../../../../org/apache/drill/exec/record/metadata/TupleMetadata.html" title="interface in org.apache.drill.exec.record.metadata">TupleMetadata</a> providedSchema()</pre> |
| <div class="block">Returns the provided schema, if defined. The provided schema is a |
| description of the source schema viewed as a Drill schema. |
| <p> |
| If a schema is provided, |
| the reader should use that schema, converting or ignoring columns |
| as needed. A scan without a provided schema has a "dynamic" schema |
| to be defined by the scan operator itself along with the column |
| projection list. |
| <p> |
| The provided schema describes the columns that the reader is |
| capable of providing. Any given query may choose to project a subset |
| of these columns.</div> |
| <dl> |
| <dt><span class="returnLabel">Returns:</span></dt> |
| <dd>the provided schema if the execution plan defines the output |
| schema, <code>null</code> if the schema should be computed dynamically |
| from the source schema and column projections</dd> |
| </dl> |
| </li> |
| </ul> |
| <a name="inputSchema--"> |
| <!-- --> |
| </a> |
| <ul class="blockList"> |
| <li class="blockList"> |
| <h4>inputSchema</h4> |
| <pre><a href="../../../../../../../../org/apache/drill/exec/record/metadata/TupleMetadata.html" title="interface in org.apache.drill.exec.record.metadata">TupleMetadata</a> inputSchema()</pre> |
| <div class="block">Returns the reader input schema: the schema which describes the |
| set of columns this reader should produce. The schema can be |
| fully dynamic (a wildcard), fully concrete (a list of columns |
| and their types) or partially dynamic (a list of columns, but some |
| types are not known.) If the reader has a choice of ways to map |
| input columns to types, the reader must choose the type specified |
| in the schema. Presumably, the specified types are those that the |
| reader is capable of providing; there is no expectation that the |
| reader will convert to arbitrary types. |
| <p> |
| If the type is <code>LATE</code> (dynamic), then the reader can choose |
| the type. Subsequent readers in the same scan will then see the |
| same column as concrete, with the type selected by the present |
| reader. |
| <p> |
| The reader is free to add additional columns. The internal mechanism |
| will just ignore those columns and return a dummy reader for them. |
| <p> |
| The reader is also free to ignore columns. In this case, the internal |
| mechanism will fill in <code>NULL</code> or default values.</div> |
| </li> |
| </ul> |
| <a name="tableSchema-org.apache.drill.exec.record.metadata.TupleMetadata-boolean-"> |
| <!-- --> |
| </a> |
| <ul class="blockList"> |
| <li class="blockList"> |
| <h4>tableSchema</h4> |
| <pre>void tableSchema(<a href="../../../../../../../../org/apache/drill/exec/record/metadata/TupleMetadata.html" title="interface in org.apache.drill.exec.record.metadata">TupleMetadata</a> schema, |
| boolean isComplete)</pre> |
| <div class="block">Specify the table schema if this is an early-schema reader. Need |
| not be called for a late-schema readers. The schema provided here, |
| if any, is a base schema: the reader is free to discover additional |
| columns during the read.</div> |
| <dl> |
| <dt><span class="paramLabel">Parameters:</span></dt> |
| <dd><code>schema</code> - the table schema if known at open time</dd> |
| <dd><code>isComplete</code> - true if the schema is complete: if it can be used |
| to define an empty schema-only batch for the first reader. Set to |
| false if the schema is partial: if the reader must read rows to |
| determine the full schema</dd> |
| </dl> |
| </li> |
| </ul> |
| <a name="tableSchema-org.apache.drill.exec.record.metadata.TupleMetadata-"> |
| <!-- --> |
| </a> |
| <ul class="blockList"> |
| <li class="blockList"> |
| <h4>tableSchema</h4> |
| <pre>void tableSchema(<a href="../../../../../../../../org/apache/drill/exec/record/metadata/TupleMetadata.html" title="interface in org.apache.drill.exec.record.metadata">TupleMetadata</a> schema)</pre> |
| </li> |
| </ul> |
| <a name="schemaIsComplete-boolean-"> |
| <!-- --> |
| </a> |
| <ul class="blockList"> |
| <li class="blockList"> |
| <h4>schemaIsComplete</h4> |
| <pre>void schemaIsComplete(boolean isComplete)</pre> |
| </li> |
| </ul> |
| <a name="batchSize-int-"> |
| <!-- --> |
| </a> |
| <ul class="blockList"> |
| <li class="blockList"> |
| <h4>batchSize</h4> |
| <pre>void batchSize(int maxRecordsPerBatch)</pre> |
| <div class="block">Set the preferred batch size (which may be overridden by the |
| result set loader in order to limit vector or batch size.)</div> |
| <dl> |
| <dt><span class="paramLabel">Parameters:</span></dt> |
| <dd><code>maxRecordsPerBatch</code> - preferred number of record per batch</dd> |
| </dl> |
| </li> |
| </ul> |
| <a name="build--"> |
| <!-- --> |
| </a> |
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| <h4>build</h4> |
| <pre><a href="../../../../../../../../org/apache/drill/exec/physical/resultSet/ResultSetLoader.html" title="interface in org.apache.drill.exec.physical.resultSet">ResultSetLoader</a> build()</pre> |
| <div class="block">Build the schema, plan the required projections and static |
| columns and return a loader used to populate value vectors. |
| If the select list includes a subset of table columns, then |
| the loader will be set up in table schema order, but the unneeded |
| column loaders will be null, meaning that the batch reader should |
| skip setting those columns.</div> |
| <dl> |
| <dt><span class="returnLabel">Returns:</span></dt> |
| <dd>the loader for the table with columns arranged in table |
| schema order</dd> |
| </dl> |
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