MySQL ORDER BY with LIMIT is the most common use of ORDER BY in interactive applications with large data sets being sorted. When you use the SELECT statement to query data from a table, the result set is not sorted. In the following example we are limiting to fetch only 3 rows from the employee table. mysql通常更愿意执行全表扫描，但是如果你用 limit 只查询几行记录的话，mysql在某些情况下可能会使用索引。 如果你将 LIMIT row_count 子句与 ORDER BY 子句组合在一起使用的话，MySQL会在找到排序结果的第一个 row_count 行后立即停止排序，而不是对整个结果进行排序。 MySQL优化：order by和limit 1.

Being able to order the result rows is particularly useful when using LIMIT, as it allows us to quickly return just the "top 3" or "bottom 10" of the results.

在Mysql中我们常常用order by来进行排序，使用limit来进行分页，当需要先排序后分页时我们往往使用类似的写法select * from 表名 order by 排序字段 limt M,N。但是这种写法却隐藏着较深的使用陷阱。在排序字段有数据重复的情况下，会很容易出现排序结果与预期不一致的问题。 Now it is only 1.23 seconds but still too long due to the early row lookups.. We, however, can trick MySQL to use the late row lookups.. We will only select the id in the subquery with an ORDER BY and LIMIT and then join the original table back on id.. Posted by: admin October 29, 2017 Leave a comment. 8.2.1.16 ORDER BY Optimization. This section describes when MySQL can use an index to satisfy an ORDER BY clause, the filesort operation used when an index cannot be used, and execution plan information available from the optimizer about ORDER BY .

MySQL TOP with ORDER BY – Example. Suboptimal MySQL ORDER BY implementation, especially together with LIMIT is often the cause of MySQL performance problems.

Here is what you need to know about MySQL ORDER BY LIMIT optimization to avoid these problems. Summary: in this tutorial, you will learn how to sort a result set using the MySQL ORDER BY clause.. Introduction to MySQL ORDER BY clause. mysql> SELECT * FROM employee LIMIT 3; +------------+-----------+----------+---------------------+-------+------------+---------------------+---------------------+ | employeeid | firstname | lastname | email | score | birthday | … For a query with an ORDER BY or GROUP BY and a LIMIT clause, the optimizer tries to choose an ordered index by default when it appears doing so would speed up query execution. How ORDER BY and LIMIT go together. Prior to MySQL 8.0.21, there was no way to override this behavior, even in cases where using some other optimization might be faster. Note that the order of values in the column1 will not change in this step, only the order … To sort the result set, you add the ORDER BY clause to the SELECT statement. order by和limit一起使用，避免引起全表扫描和数据排序是非常重要的，因此借助合适的索引提高查询效率。 使用联合索引 联合索引又叫复合索引，是由表中的几个列联合组成的索引。

How does ORDER BY work? The ORDER BY clause goes after the FROM clause but before the LIMIT.