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Yang, Tong
6182f91ba8
Reviewed-by: Hasko, Vladimir <vladimir.hasko@t-systems.com> Co-authored-by: Yang, Tong <yangtong2@huawei.com> Co-committed-by: Yang, Tong <yangtong2@huawei.com>
52 lines
6.1 KiB
HTML
52 lines
6.1 KiB
HTML
<a name="mrs_01_1432"></a><a name="mrs_01_1432"></a>
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<h1 class="topictitle1">DROP COLUMNS</h1>
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<div id="body1595920211938"><div class="section" id="mrs_01_1432__s494ddc1dd7e2490eb063c8ce529cc452"><h4 class="sectiontitle">Function</h4><p id="mrs_01_1432__a5506d5ecc6ea4e9ca5b59a2222ac9501">This command is used to delete one or more columns from a table.</p>
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</div>
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<div class="section" id="mrs_01_1432__s59188cabaa794a428ef0688f8f6bad24"><h4 class="sectiontitle">Syntax</h4><p id="mrs_01_1432__a3962158458ef450d977754c31013714e"><b><span class="cmdname" id="mrs_01_1432__cmdname14292114119143">ALTER TABLE</span></b> <i><span class="varname" id="mrs_01_1432__v7c2993bbf6a54a6abec620957a9940a7">[db_name.]table_name</span></i> <b><span class="cmdname" id="mrs_01_1432__cmdname12387460148">DROP COLUMNS</span></b> <i><span class="varname" id="mrs_01_1432__v789e9e06435f423aa2d8f9844ce374cd">(col_name, ...)</span></i>;</p>
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</div>
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<div class="section" id="mrs_01_1432__s740c62e2bdba42fbbfde99f918aea831"><h4 class="sectiontitle">Parameter Description</h4>
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<div class="tablenoborder"><table cellpadding="4" cellspacing="0" summary="" id="mrs_01_1432__t1a037221ea024e24bc444cef27b030f5" frame="border" border="1" rules="all"><caption><b>Table 1 </b>DROP COLUMNS parameters</caption><thead align="left"><tr id="mrs_01_1432__rb11890d74bf34c84b71038cb1f7194e0"><th align="left" class="cellrowborder" valign="top" width="19.439999999999998%" id="mcps1.3.3.2.2.3.1.1"><p id="mrs_01_1432__ab5005c2bf1aa4617aab0282131f514a9">Parameter</p>
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</th>
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<th align="left" class="cellrowborder" valign="top" width="80.56%" id="mcps1.3.3.2.2.3.1.2"><p id="mrs_01_1432__a239f651d72f64266bc847166563d18db">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_1432__rae513e62727c4ff59af1c53da40afa2a"><td class="cellrowborder" valign="top" width="19.439999999999998%" headers="mcps1.3.3.2.2.3.1.1 "><p id="mrs_01_1432__aa500769b84dd4bd0bd245e0ca95e4dc7">db_name</p>
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</td>
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<td class="cellrowborder" valign="top" width="80.56%" headers="mcps1.3.3.2.2.3.1.2 "><p id="mrs_01_1432__a94cccab87a4c4876ad174bb6ad2c4d4f">Database name. If this parameter is not specified, the current database is selected.</p>
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</td>
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</tr>
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<tr id="mrs_01_1432__rfad5b30e64eb4740b95e11d0b4789130"><td class="cellrowborder" valign="top" width="19.439999999999998%" headers="mcps1.3.3.2.2.3.1.1 "><p id="mrs_01_1432__a15255f01bf7540e0a0c2cc3336263986">table_name</p>
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</td>
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<td class="cellrowborder" valign="top" width="80.56%" headers="mcps1.3.3.2.2.3.1.2 "><p id="mrs_01_1432__af7869093ad50436999fb18be5eeada3e">Table name.</p>
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</td>
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</tr>
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<tr id="mrs_01_1432__r12d76c3b8ebb49fcaa5024c835f850a7"><td class="cellrowborder" valign="top" width="19.439999999999998%" headers="mcps1.3.3.2.2.3.1.1 "><p id="mrs_01_1432__a7890c0e708e040539cfc5593ba7692ad">col_name</p>
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</td>
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<td class="cellrowborder" valign="top" width="80.56%" headers="mcps1.3.3.2.2.3.1.2 "><p id="mrs_01_1432__a74f0e93f169d40f3a6c73f54dd24f6ed">Name of a column in a table. Multiple columns are supported. It consists of letters, digits, and underscores (_).</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_1432__s66beba64f4b64d00af01667c2d5fa261"><h4 class="sectiontitle">Precautions</h4><p id="mrs_01_1432__p2456182111118">After a column is deleted, at least one key column must exist in the schema. Otherwise, an error message is displayed, and the column fails to be deleted.</p>
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</div>
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<div class="section" id="mrs_01_1432__s4a8c07d2a6814105b00a2104cc888dec"><h4 class="sectiontitle">Examples</h4><p id="mrs_01_1432__a3be80f9414c943aab4a7c1343115316a">Assume that the table contains four columns named a1, b1, c1, and d1.</p>
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<ul id="mrs_01_1432__u612a860e51a14547a9cb638f5b80f43f"><li id="mrs_01_1432__l9f290ec263c047cd91251b5112184074">Delete a column:<p id="mrs_01_1432__ada392616bd4049adba24b7b90ddd1a4f"><a name="mrs_01_1432__l9f290ec263c047cd91251b5112184074"></a><a name="l9f290ec263c047cd91251b5112184074"></a><b><span class="cmdname" id="mrs_01_1432__cmdname16371452151410">ALTER TABLE</span></b> <i><span class="varname" id="mrs_01_1432__vd5f4d6cc6e7c4b10911a8e84f9161d7d">carbon</span></i> <b><span class="cmdname" id="mrs_01_1432__cmdname899035591410">DROP COLUMNS</span></b> <i><span class="varname" id="mrs_01_1432__vf8e2984f6b1a45c89fa4bb931d4c15f2">(b1)</span></i>;</p>
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<p id="mrs_01_1432__ad0054b4b883e4e7ca6ff754054e79516"><b><span class="cmdname" id="mrs_01_1432__cmdname1583211017158">ALTER TABLE</span></b> <i><span class="varname" id="mrs_01_1432__vd57ff232d05a46c2868fdd48ec989c7f">test_db.carbon</span></i> <b><span class="cmdname" id="mrs_01_1432__cmdname117774181513">DROP COLUMNS</span></b> <i><span class="varname" id="mrs_01_1432__v4d1fdd6c4e69478ca465cba6acab0806">(b1)</span></i>;</p>
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</li><li id="mrs_01_1432__l47d9b32dbc9b4c228a78914f2934e464">Delete multiple columns:<p id="mrs_01_1432__a76c0ccecbb994aee8d380dd2c9609335"><a name="mrs_01_1432__l47d9b32dbc9b4c228a78914f2934e464"></a><a name="l47d9b32dbc9b4c228a78914f2934e464"></a><b><span class="cmdname" id="mrs_01_1432__cmdname28635761511">ALTER TABLE</span></b> <i><span class="varname" id="mrs_01_1432__v0d348c5d92894dbe9d2df0ed6bba4dbf">carbon</span></i> <b><span class="cmdname" id="mrs_01_1432__cmdname1287141116152">DROP COLUMNS</span></b> <i><span class="varname" id="mrs_01_1432__v879e2eed46e549189072c2a8d7a4b3aa">(b1,c1)</span></i>;</p>
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<p id="mrs_01_1432__a61696a76a68e4104a32a1c9e847ca50d"><b><span class="cmdname" id="mrs_01_1432__cmdname2877315121512">ALTER TABLE</span></b> <i><span class="varname" id="mrs_01_1432__v3d1e595844554d798bd003e7f97f28ab">test_db.carbon</span></i> <b><span class="cmdname" id="mrs_01_1432__cmdname1925791911153">DROP COLUMNS</span></b> <i><span class="varname" id="mrs_01_1432__v3522a13048854b42b2d6f28ba1d54aed">(b1,c1)</span></i>;</p>
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</li></ul>
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</div>
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<div class="section" id="mrs_01_1432__s5cc5c1837dd4409f9e8d6f22ec7ebe44"><h4 class="sectiontitle">System Response</h4><p id="mrs_01_1432__a272107c5f85b47a8bcfb9fab9936fa9e">If you run the <strong id="mrs_01_1432__b5462117141012">DESCRIBE</strong> command, the deleted columns will not be displayed.</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_1424.html">DDL</a></div>
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</div>
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</div>
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