union union all哪个效率高
时间: 2023-09-07 09:16:43 浏览: 103
MySQL中使用or、in与union all在查询命令下的效率对比
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根据引用和引用的内容,可以得出结论:UNION ALL的效率要比UNION高很多。UNION操作会去重,而UNION ALL不会去重。由于UNION操作需要进行去重操作,因此在数据量较大、连表数量较多的情况下,UNION的效率会比较低。相比之下,UNION ALL不需要进行去重操作,因此在合并结果集时会更快。所以,如果可以确认合并的两个结果集中不包含重复的数据,建议使用UNION ALL来提高查询效率。引用<span class="em">1</span><span class="em">2</span><span class="em">3</span>
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