forked from docs/doc-exports
Yang, Tong
48706b7552
Reviewed-by: Kacur, Michal <michal.kacur@t-systems.com> Co-authored-by: Yang, Tong <yangtong2@huawei.com> Co-committed-by: Yang, Tong <yangtong2@huawei.com>
67 lines
6.7 KiB
HTML
67 lines
6.7 KiB
HTML
<a name="mrs_01_24499"></a><a name="mrs_01_24499"></a>
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<h1 class="topictitle1">Altering a Column</h1>
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<div id="body0000001585034889"><div class="section" id="mrs_01_24499__en-us_topic_0265792790_sa1cb229bf26b4a7a8efd1716defb63de"><h4 class="sectiontitle">Function</h4><p id="mrs_01_24499__en-us_topic_0265792790_ac917e6d6e78044e99179c0e0f5284232">The <strong id="mrs_01_24499__b1652113223131">ALTER TABLE ... ALTER COLUMN</strong> command is used to change the attributes of a column, such as the column type, position, and comment.</p>
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</div>
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<div class="section" id="mrs_01_24499__en-us_topic_0265792790_sc019b10a59e9426498a678c024d74f03"><h4 class="sectiontitle">Syntax</h4><p id="mrs_01_24499__p115411424114818"><strong id="mrs_01_24499__b5541132404813">ALTER TABLE </strong><em id="mrs_01_24499__i8752171611276">Table name</em> <strong id="mrs_01_24499__b14541142454811">ALTER</strong></p>
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<p id="mrs_01_24499__p2071145618449"><strong id="mrs_01_24499__b8767101664815">[COLUMN] </strong><em id="mrs_01_24499__i76601519192719">col_old_name</em> <strong id="mrs_01_24499__b420420555315">TYPE</strong><em id="mrs_01_24499__i72041055163116"> column_type</em></p>
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<p id="mrs_01_24499__p9766727204812"><strong id="mrs_01_24499__b1586155814910">[COMMENT] </strong><em id="mrs_01_24499__i777772272716">col_comment</em></p>
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<p id="mrs_01_24499__p165085319489"><strong id="mrs_01_24499__b71811522504">[FIRST|AFTER] </strong><em id="mrs_01_24499__i1813417262274">column_name</em></p>
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</div>
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<div class="section" id="mrs_01_24499__en-us_topic_0265792790_s253f086de08745ac890027c0b103cd7a"><h4 class="sectiontitle">Parameter Description</h4>
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<div class="tablenoborder"><table cellpadding="4" cellspacing="0" summary="" id="mrs_01_24499__en-us_topic_0265792790_ta69e9ecdc1554375a8a1e844b14e00c5" frame="border" border="1" rules="all"><caption><b>Table 1 </b>ALTER COLUMN parameters</caption><thead align="left"><tr id="mrs_01_24499__en-us_topic_0265792790_r61ddb6139b8d4f4ca4a88c6389f8f327"><th align="left" class="cellrowborder" valign="top" width="30%" id="mcps1.3.3.2.2.3.1.1"><p id="mrs_01_24499__en-us_topic_0265792790_aeb0bfa560fb74f1f9e584cc1ef05bb9b">Parameter</p>
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</th>
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<th align="left" class="cellrowborder" valign="top" width="70%" id="mcps1.3.3.2.2.3.1.2"><p id="mrs_01_24499__en-us_topic_0265792790_ae81789e97e6d4953a8342f22d64feea9">Description</p>
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</th>
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</tr>
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</thead>
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<tbody><tr id="mrs_01_24499__en-us_topic_0265792790_r4a578c7015ba461bab46a5c40c46256a"><td class="cellrowborder" valign="top" width="30%" headers="mcps1.3.3.2.2.3.1.1 "><p id="mrs_01_24499__en-us_topic_0265792790_ac25da7f69c964d93947693ed5b4006cb">tableName</p>
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</td>
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<td class="cellrowborder" valign="top" width="70%" headers="mcps1.3.3.2.2.3.1.2 "><p id="mrs_01_24499__en-us_topic_0265792790_a09288a5af7f44e36922b37de34446d94">Table name.</p>
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</td>
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</tr>
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<tr id="mrs_01_24499__row11891114814"><td class="cellrowborder" valign="top" width="30%" headers="mcps1.3.3.2.2.3.1.1 "><p id="mrs_01_24499__p2181318482">col_old_name</p>
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</td>
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<td class="cellrowborder" valign="top" width="70%" headers="mcps1.3.3.2.2.3.1.2 "><p id="mrs_01_24499__p18189110483">Name of the column to be altered.</p>
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</td>
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</tr>
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<tr id="mrs_01_24499__row7604329174817"><td class="cellrowborder" valign="top" width="30%" headers="mcps1.3.3.2.2.3.1.1 "><p id="mrs_01_24499__p116053297485">column_type</p>
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</td>
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<td class="cellrowborder" valign="top" width="70%" headers="mcps1.3.3.2.2.3.1.2 "><p id="mrs_01_24499__p186051829144818">Type of the target column.</p>
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</td>
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</tr>
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<tr id="mrs_01_24499__row1051610168493"><td class="cellrowborder" valign="top" width="30%" headers="mcps1.3.3.2.2.3.1.1 "><p id="mrs_01_24499__p0516181634919">col_comment</p>
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</td>
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<td class="cellrowborder" valign="top" width="70%" headers="mcps1.3.3.2.2.3.1.2 "><p id="mrs_01_24499__p175171216144918">Column comment.</p>
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</td>
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</tr>
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<tr id="mrs_01_24499__row526813764915"><td class="cellrowborder" valign="top" width="30%" headers="mcps1.3.3.2.2.3.1.1 "><p id="mrs_01_24499__p926817376491">column_name</p>
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</td>
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<td class="cellrowborder" valign="top" width="70%" headers="mcps1.3.3.2.2.3.1.2 "><p id="mrs_01_24499__p1326853704916">New position to place the target column. For example, <strong id="mrs_01_24499__b44031125111718">AFTER column_name</strong> indicates that the target column is placed after <strong id="mrs_01_24499__b168261244191719">column_name</strong>.</p>
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</td>
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</tr>
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</tbody>
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</table>
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</div>
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</div>
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<div class="section" id="mrs_01_24499__en-us_topic_0265792790_s55536c9c534643ed8272f9f4b47fb407"><h4 class="sectiontitle">Example</h4><ul id="mrs_01_24499__ul63722051112818"><li id="mrs_01_24499__li43721651142818">Changing the column type<pre class="screen" id="mrs_01_24499__screen1963611232294">ALTER TABLE table1 ALTER COLUMN a.b.c TYPE bigint</pre>
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<p id="mrs_01_24499__p6526204742817"><strong id="mrs_01_24499__b19656145916249">a.b.c</strong> indicates the full path of a nested column. For details about the nested column rules, see <a href="mrs_01_24498.html">Adding a Column</a>.</p>
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<p id="mrs_01_24499__p1552644762810">The following changes on column types are supported:</p>
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<ul id="mrs_01_24499__ul1110004412314"><li id="mrs_01_24499__li161249414314">int => long/float/double/string/decimal</li><li id="mrs_01_24499__li20126184193119">long => float/double/string/decimal</li><li id="mrs_01_24499__li3127134163119">float => double/String/decimal</li><li id="mrs_01_24499__li1127941193114">From double to string or decimal</li><li id="mrs_01_24499__li1613084143119">From decimal to decimal or string</li><li id="mrs_01_24499__li1995628125019">From string to date or decimal</li><li id="mrs_01_24499__li8131941183118">From date to string</li></ul>
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</li><li id="mrs_01_24499__li18227043306">Altering other attributes<pre class="screen" id="mrs_01_24499__screen122214179304">ALTER TABLE table1 ALTER COLUMN a.b.c DROP NOT NULL
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ALTER TABLE table1 ALTER COLUMN a.b.c COMMENT 'new comment'
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ALTER TABLE table1 ALTER COLUMN a.b.c FIRST
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ALTER TABLE table1 ALTER COLUMN a.b.c AFTER x</pre>
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<p id="mrs_01_24499__p952514717288"><strong id="mrs_01_24499__b175358301350">a.b.c</strong> indicates the full path of a nested column. For details about the nested column rules, see <a href="mrs_01_24498.html">Adding a Column</a>.</p>
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</li></ul>
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</div>
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<div class="section" id="mrs_01_24499__en-us_topic_0265792790_sbd5eea8637c94038bf6a129ab9ca129f"><h4 class="sectiontitle">Response</h4><p id="mrs_01_24499__en-us_topic_0265792790_ab3f2ebd199c342fb9103cbe4f02c7148">You can run the <strong id="mrs_01_24499__b1689810301694">DESCRIBE</strong> command to view the modified column.</p>
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</div>
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</div>
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<div>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="mrs_01_24495.html">SparkSQL Schema Evolution and Syntax Description</a></div>
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</div>
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