<blockquote>正确做法是转换查询条件值而非索引列，避免在WHERE中对索引列使用函数，应使用FROM_UNIXTIME或UNIX_TIMESTAMP转换比较值以利用索引，提升查询效率。</blockquote> <p><img src=”https://img.php.cn/upload/article/001/503/042/175556274447293.jpeg” alt=”mysql日期与时间戳互转方法 where条件查询优化方案”></p> <p>在MySQL中，日期与时间戳之间的转换其实非常直接，通常通过<div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>UNIX_TIMESTAMP()</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div>和<div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>FROM_UNIXTIME()</pre><div class=”contentsignin”></div></div>这两个函数来完成。但真正的性能挑战，或者说我们经常会踩的坑，往往出现在将这些转换操作应用到<div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>WHERE</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div>子句中时。优化这类查询的关键在于，永远不要对被索引的列使用函数进行操作，而是应该转换你的比较值。</p> <h3>解决方案</h3> <p>日期时间与时间戳的互转：</p> <ul> <li> <strong>日期时间转时间戳：</strong> 使用 <div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>UNIX_TIMESTAMP(date_expression)</pre><div class=”contentsignin”></div></div>。例如，<div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>SELECT UNIX_TIMESTAMP(‘2023-10-26 10:30:00’);</pre><div class=”contentsignin”></div></div> 会返回一个整数时间戳。如果你有一个 <div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>DATETIME</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div> 或 <div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>TIMESTAMP</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div> 类型的列，直接传入即可。</li> <li> <strong>时间戳转日期时间：</strong> 使用 <div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>FROM_UNIXTIME(unix_timestamp)</pre><div class=”contentsignin”></div></div>。例如，<div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>SELECT FROM_UNIXTIME(1678886400);</pre><div class=”contentsignin”></div></div> 会返回一个 <div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>DATETIME</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div> 格式的字符串，通常是 <div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>YYYY-MM-DD HH:MM:SS</pre><div class=”contentsignin”></div></div>。</li> </ul> <p><strong><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>WHERE</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div> 条件查询优化方案的核心：</strong></p> <p>避免在 <div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>WHERE</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div> 子句中对索引列使用任何函数。这意味着，如果你有一个名为 <div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>created_at</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div> 的 <div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>DATETIME</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div> 列并且它有索引，那么 <div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>WHERE UNIX_TIMESTAMP(created_at) > 1678886400</pre><div class=”contentsignin”></div></div> 这样的写法是极度低效的。正确的做法是转换你的查询条件值，而不是被查询的列。</p> <p><strong>示例：</strong></p> <p>假设你有一个 <div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>orders</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div> 表，其中有一个 <div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>created_at</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div> (DATETIME类型，已建立索引) 列，你想查询某个时间戳之后的所有订单。</p> <ul> <li> <p><strong>错误示范 (会使索引失效):</strong></p><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=’brush:sql;toolbar:false;’>SELECT * FROM orders WHERE UNIX_TIMESTAMP(created_at) > 1678886400;</pre><div class=”contentsignin”></div></div><p>这条查询会让MySQL对 <div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>created_at</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div> 列的每一行都执行 <div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>UNIX_TIMESTAMP()</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div> 函数，然后进行比较，这等同于全表扫描。</p> </li> <li> <p><strong>正确示范 (利用索引):</strong></p><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=’brush:sql;toolbar:false;’>SELECT * FROM orders WHERE created_at > FROM_UNIXTIME(1678886400);</pre><div class=”contentsignin”></div></div><p>这里，我们把时间戳 <div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>1678886400</pre><div class=”contentsignin”></div></div> 转换成 <div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>DATETIME</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div> 格式，然后与 <div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>created_at</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div> 列直接比较。由于 <div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>created_at</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div> 列没有被函数处理，MySQL可以有效地使用其上的索引进行快速查找。</p> </li> </ul> <p>同样的道理，如果你有一个 <div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>timestamp_col</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div> (INT或BIGINT类型，存储时间戳，已建立索引) 列，你想查询某个日期之后的所有数据：</p> <ul> <li> <p><strong>错误示范 (会使索引失效):</strong></p><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=’brush:sql;toolbar:false;’>SELECT * FROM my_table WHERE FROM_UNIXTIME(timestamp_col) > ‘2023-03-15 00:00:00’;</pre><div class=”contentsignin”></div></div></li> <li> <p><strong>正确示范 (利用索引):</strong></p><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=’brush:sql;toolbar:false;’>SELECT * FROM my_table WHERE timestamp_col > UNIX_TIMESTAMP(‘2023-03-15 00:00:00’);</pre><div class=”contentsignin”></div></div></li> </ul> <h3> <a >为什么</a>在WHERE条件中使用函数会影响查询性能？</h3> <p>这其实是个经典问题，也是很多初学者甚至经验丰富的开发者偶尔会忽略的细节。简单来说，当你对一个被索引的列应用函数时，MySQL的查询优化器就无法利用该列上的索引了。索引，尤其是B-tree索引，其核心在于数据是有序存储的。例如，一个日期列的索引是按照日期大小排序的。当你用 <div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>UNIX_TIMESTAMP(date_column)</pre><div class=”contentsignin”></div></div> 去查询时，你实际上是把 <div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>date_column</pre><div class=”contentsignin”></div></div> 的值“扭曲”了，它不再是索引中那个有序的、可以直接查找的值。</p> <p>想象一下，你有一本按照姓氏首字母排序的电话簿（这就是索引），现在你突然想找一个名字，但你只知道这个名字的MD5哈希值。你不可能通过哈希值去查这本按姓氏排序的电话簿，对吧？你只能把电话簿里所有的名字都计算一遍MD5哈希值，然后逐个比较。这就是全表扫描的代价。MySQL在遇到这种情况时，不得不放弃使用索引，转而执行全表扫描，然后对每一行数据执行你的函数，再进行比较，这效率自然就下去了。特别是在数据量很大的时候，这种性能损耗是灾难性的。</p> <h3>如何正确利用索引优化日期/时间戳的范围查询？</h3> <p>除了上面提到的转换比较值，针对日期/时间戳的范围查询，我们还有一些非常实用的策略来确保索引的有效利用。我的经验告诉我，范围查询是这类数据类型最常见的查询模式，所以掌握好这部分至关重要。</p> <p>首先，继续强调核心原则：<strong>确保索引列本身不被函数处理。</strong></p> <p>对于日期范围查询，<div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>BETWEEN</pre><div class=”contentsignin”></div></div> 操作符是一个非常简洁且高效的选择，因为它天然地支持利用索引。</p> <p><strong>示例：查询某个日期区间内的订单</strong></p> <p>假设我们要查询2023年10月1日到2023年10月31日之间的所有订单。</p> <ul> <li> <p><strong>使用 <div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>DATETIME</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div> 或 <div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>TIMESTAMP</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div> 列 (推荐):</strong></p><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=’brush:sql;toolbar:false;’>SELECT * FROM orders WHERE created_at BETWEEN ‘2023-10-01 00:00:00’ AND ‘2023-10-31 23:59:59’;</pre><div class=”contentsignin”></div></div><p>或者更精确地处理日期边界：</p><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=’brush:sql;toolbar:false;’>SELECT * FROM orders WHERE created_at >= ‘2023-10-01 00:00:00’ AND created_at < ‘2023-11-01 00:00:00’;</pre><div class=”contentsignin”></div></div><p>这种写法对于 <div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>DATETIME</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div> 和 <div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>TIMESTAMP</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div> 类型非常友好，并且能够充分利用 <div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>created_at</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div> 列上的索引。</p> </li> <li> <p><strong>使用 <div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>INT</pre><div class=”contentsignin”></div></div> 或 <div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>BIGINT</pre><div class=”contentsignin”></div></div> 存储时间戳的列:</strong></p><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=’brush:sql;toolbar:false;’>SELECT * FROM my_table WHERE timestamp_col BETWEEN UNIX_TIMESTAMP(‘2023-10-01 00:00:00’) AND UNIX_TIMESTAMP(‘2023-10-31 23:59:59’);</pre><div class=”contentsignin”></div></div><p>同样，也可以使用 <div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>>=</pre><div class=”contentsignin”></div></div> 和 <div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”><</pre><div class=”contentsignin”></div></div> 的组合：</p><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=’brush:sql;toolbar:false;’>SELECT * FROM my_table WHERE timestamp_col >= UNIX_TIMESTAMP(‘2023-10-01 00:00:00’) AND timestamp_col < UNIX_TIMESTAMP(‘2023-11-01 00:00:00’);</pre><div class=”contentsignin”></div></div><p>这两种方法都将日期字符串转换为时间戳，确保了 <div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>timestamp_col</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div> 列在比较时保持其原始的、可被索引利用的形式。</p> </li> </ul> <p>此外，如果你的日期列是 <div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>DATE</pre><div class=”contentsignin”></div></div> 类型，那么查询一整天的数据通常是直接比较：</p><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=’brush:sql;toolbar:false;’>SELECT * FROM daily_records WHERE record_date = ‘2023-10-26’;</pre><div class=”contentsignin”></div></div><p>或者查询一个日期范围：</p><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=’brush:sql;toolbar:false;’>SELECT * FROM daily_records WHERE record_date BETWEEN ‘2023-10-01’ AND ‘2023-10-31’;</pre><div class=”contentsignin”></div></div><p>这些操作都能很好地利用 <div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>record_date</pre><div class=”contentsignin”></div></div> 上的索引。关键就是，让MySQL在做比较时，看到的始终是索引列的原始值，而不是经过函数处理后的结果。</p> <h3>除了索引，还有哪些策略可以提升日期/时间相关查询的效率？</h3> <p>仅仅依赖索引有时还不够，尤其是在处理海量数据或面临复杂查询场景时。我个人在实践中，除了优化索引的使用，还会考虑以下几点来进一步提升日期/时间相关查询的效率：</p> <p><strong>1. 数据分区 (Partitioning):</strong> 当你的表非常庞大，比如历史数据按日期持续增长，那么数据分区就成了非常有力的<a >工具</a>。你可以根据日期字段（例如 <div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>created_at</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div> 的年份或月份）对表进行分区。这样，当你的查询条件限定在某个日期范围内时，MySQL只需要扫描对应的一个或几个分区，而不是整个表。这能极大地缩小查询范围，提高效率。</p> <p>比如，一个按年份分区的 <div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>orders</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div> 表，当你查询2023年的订单时，数据库就只去访问2023年的那个物理文件，其他年份的数据完全不用碰。这个效果，比单纯的索引扫描要快得多，因为它直接减少了I/O量。当然，分区策略需要提前规划好，一旦实施，修改起来会比较麻烦。</p> <p><strong>2. 覆盖索引 (Covering Index):</strong> 如果你的查询只需要从表中获取日期/时间相关的列以及其他几个被索引的列，那么创建一个覆盖索引会非常高效。覆盖索引是指一个索引包含了查询所需的所有列，这样MySQL就无需回表（即无需访问实际的数据行）就能获取所有需要的数据。</p> <p>例如，如果你经常查询 <div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>created_at</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div> 和 <div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>user_id</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div>，并且 <div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>user_id</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div> 也在索引中，那么一个包含 <div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>(created_at, user_id)</pre><div class=”contentsignin”></div></div> 的复合索引，如果查询只涉及到这两列，就可以成为覆盖索引。查询速度会显著提升，因为所有数据都直接从索引中读取，避免了昂贵的磁盘随机I/O操作。</p> <p><strong>3. 适当的冗余字段 (Denormalization):</strong> 在某些极端情况下，为了优化查询，你可能会考虑在表中增加一些冗余的日期相关字段。比如，如果你的 <div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>created_at</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div> 是 <div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>DATETIME</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div> 类型，但你经常需要按年份、月份或日期进行分组或查询，你可以考虑增加 <div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>created_year</pre><div class=”contentsignin”></div></div> (INT), <div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>created_month</pre><div class=”contentsignin”></div></div> (TINYINT), <div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>created_day</pre><div class=”contentsignin”></div></div> (TINYINT) 等字段，并在这些字段上建立索引。</p> <p>这是一种典型的空间换时间策略。虽然增加了存储空间和数据写入时的维护成本（你需要在插入或更新时同步这些冗余字段），但对于读密集型应用来说，它能极大地简化查询并提高性能，因为它避免了在查询时对 <div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>created_at</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div> 进行 <div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>YEAR()</pre><div class=”contentsignin”></div></div>, <div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>MONTH()</pre><div class=”contentsignin”></div></div>, <div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>DAY()</pre><div class=”contentsignin”></div></div> 等函数操作。当然，这需要权衡，不适合所有场景。</p> <p>这些策略都是在索引优化基础之上，根据具体业务场景和数据量级来选择性使用的。没有银弹，但结合起来，往往能解决大部分日期/时间查询的性能瓶颈。</p>
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