forked from docs/doc-exports
Su, Xiaomeng
04d4597cf3
Reviewed-by: Pruthi, Vineet <vineet.pruthi@t-systems.com> Co-authored-by: Su, Xiaomeng <suxiaomeng1@huawei.com> Co-committed-by: Su, Xiaomeng <suxiaomeng1@huawei.com>
28 lines
5.5 KiB
HTML
28 lines
5.5 KiB
HTML
<a name="dli_08_0178"></a><a name="dli_08_0178"></a>
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<h1 class="topictitle1">Multi-Layer Nested Subquery</h1>
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<div id="body8662426"><div class="section" id="dli_08_0178__en-us_topic_0093946805_sadd1395b72534a3e893bd54ed76a63e3"><h4 class="sectiontitle">Function</h4><p id="dli_08_0178__en-us_topic_0093946805_a910f16e1d885458a89cf140ad9994945">This statement is used to nest queries in the subquery. </p>
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<div class="section" id="dli_08_0178__en-us_topic_0093946805_s8454fb8edda04b3692dac531665a3cda"><h4 class="sectiontitle">Syntax</h4><div class="codecoloring" codetype="Sql" id="dli_08_0178__screen68494019427"><div class="highlight"><table class="highlighttable"><tr><td class="linenos"><div class="linenodiv"><pre><span class="normal">1</span></pre></div></td><td class="code"><div><pre><span></span><span class="k">SELECT</span><span class="w"> </span><span class="n">attr_expr</span><span class="w"> </span><span class="k">FROM</span><span class="w"> </span><span class="p">(</span><span class="w"> </span><span class="k">SELECT</span><span class="w"> </span><span class="n">attr_expr</span><span class="w"> </span><span class="k">FROM</span><span class="w"> </span><span class="p">(</span><span class="w"> </span><span class="k">SELECT</span><span class="w"> </span><span class="n">attr_expr</span><span class="w"> </span><span class="k">FROM</span><span class="p">...</span><span class="w"> </span><span class="p">...</span><span class="w"> </span><span class="p">)</span><span class="w"> </span><span class="p">[</span><span class="k">alias</span><span class="p">]</span><span class="w"> </span><span class="p">)</span><span class="w"> </span><span class="p">[</span><span class="k">alias</span><span class="p">];</span>
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</pre></div></td></tr></table></div>
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<div class="section" id="dli_08_0178__en-us_topic_0093946805_seedf07c71d9d4c1fbd3b6aa0900d8a86"><h4 class="sectiontitle">Keyword</h4><ul id="dli_08_0178__en-us_topic_0093946805_u277c0d782c6b4eaf920e032c5ae01526"><li id="dli_08_0178__en-us_topic_0093946805_l3ba885c73532480f911b0ed3f0ce6b94">All is used to return repeated rows. By default, all repeated rows are returned. It is followed by asterisks (*) only. Otherwise, an error will occur.</li><li id="dli_08_0178__en-us_topic_0093946805_l9a577de3f5d847e8903cfb313328a7eb">DISTINCT is used to remove the repeated line from the result.</li></ul>
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<div class="section" id="dli_08_0178__en-us_topic_0093946805_sbca6dfa6de1643718664563dd2103c13"><h4 class="sectiontitle">Precautions</h4><ul id="dli_08_0178__en-us_topic_0093946805_u5a044b556ac24272b1bfb5a1e8fcc149"><li id="dli_08_0178__en-us_topic_0093946805_l7965ec0e2c04471ca798cf8773f0979b">The to-be-queried table must exist. If this statement is used to query a table that does not exist, an error is reported. </li><li id="dli_08_0178__en-us_topic_0093946805_l42270f78a35f4bb98be670e01d44f919">The alias of the subquery must be specified in the nested query. Otherwise, an error is reported. </li><li id="dli_08_0178__en-us_topic_0093946805_l9c9f291f4542416790223ca78884d148">The alias must be specified before the running of the statement. Otherwise, an error is reported. It is advised to specify a unique alias. </li></ul>
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<div class="section" id="dli_08_0178__en-us_topic_0093946805_s425c730bfc374bb6be605d452861884f"><h4 class="sectiontitle">Example</h4><p id="dli_08_0178__en-us_topic_0093946805_abe02c05396ba487599729d5a2fb5f772">To return the name field from the <strong id="dli_08_0178__b41879571333">user_info</strong> table after three queries, run the following statement:</p>
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<div class="codecoloring" codetype="Sql" id="dli_08_0178__screen1183113593423"><div class="highlight"><table class="highlighttable"><tr><td class="linenos"><div class="linenodiv"><pre><span class="normal">1</span></pre></div></td><td class="code"><div><pre><span></span><span class="k">SELECT</span><span class="w"> </span><span class="n">name</span><span class="w"> </span><span class="k">FROM</span><span class="w"> </span><span class="p">(</span><span class="w"> </span><span class="k">SELECT</span><span class="w"> </span><span class="n">name</span><span class="p">,</span><span class="w"> </span><span class="n">acc_num</span><span class="w"> </span><span class="k">FROM</span><span class="w"> </span><span class="p">(</span><span class="w"> </span><span class="k">SELECT</span><span class="w"> </span><span class="n">name</span><span class="p">,</span><span class="w"> </span><span class="n">acc_num</span><span class="p">,</span><span class="w"> </span><span class="n">password</span><span class="w"> </span><span class="k">FROM</span><span class="w"> </span><span class="p">(</span><span class="w"> </span><span class="k">SELECT</span><span class="w"> </span><span class="n">name</span><span class="p">,</span><span class="w"> </span><span class="n">acc_num</span><span class="p">,</span><span class="w"> </span><span class="n">password</span><span class="p">,</span><span class="w"> </span><span class="n">bank_acc</span><span class="w"> </span><span class="k">FROM</span><span class="w"> </span><span class="n">user_info</span><span class="p">)</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="p">)</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="p">)</span><span class="w"> </span><span class="k">c</span><span class="p">;</span>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="dli_08_0174.html">Subquery</a></div>
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