DISTINCT和Using Temporary的关系 DISTINCT关键字和Using Temporary标志之间存在一定的关联。当我们在查询中使用DISTINCT关键字时,如果MySQL无法直接使用索引来完成查询,它就可能会创建一个临时表来处理数据。 下面是一个使用DISTINCT关键字和Using Temporary标志的示例: EXPLAIN SELECT DISTINCT column1, column2 FROM table;...
信息种类:Using filesort 、Using temporary 、Using index 、Using where 、Using join buffer 、impossible where 、select tables optimized away 、distinct Using filesort(需要优化) 说明mysql会对数据使用一个外部的索引排序,而不是按照表内的索引顺序进行读取。MySQL中无法利用索引完成的排序操作称为"文件排序" ...
Using DISTINCT to Eliminate Duplicates Problem You want to know which values are present in a set of values, without listing duplicate values a bunch of times. Or you want … - Selection from MySQL Cookbook [Book]
For example, these statements are distinct from each other: SELECT first_name, last_name FROM customer WHERE customer_id = 1; select first_name, last_name from customer where customer_id = 99; SELECT first_name, last_name FROM customer WHERE customer_id = 143; But all of them have ...
distinct 去重复 having 条件筛选 is not null 去空 -- 表连接实现-- 第一步:右连接获取有成绩的地区mysql>selectstuaddressfromstuinforightjoinstumarksusing(stuno);+---+|stuaddress|+---+|北京||上海||天津||北京||天津||NULL|+---+# `6rowsinset(0.00sec)`-- 第二步:去重复mysql>selectdistinc...
Summary: in this tutorial, you will learn how to use MySQL DISTINCT clause with the SELECT statement to eliminate duplicate rows in a result set.Introduction to MySQL DISTINCT clause#When querying data from a table, you may get duplicate rows. In order to remove these duplicate rows, you ...
With theCOLLATEclause, you can override whatever the default collation is for a comparison.COLLATEmay be used in various parts of SQL statements. Here are some examples: WithORDER BY: SELECTkFROMt1ORDERBYkCOLLATElatin1_german2_ci; WithAS: ...
Re: How to query this using distinct? Bob Field June 27, 2006 08:54AM Sorry, you can't reply to this topic. It has been closed.Content reproduced on this site is the property of the respective copyright holders. It is not reviewed in advance by Oracle and does not necessarily represent...
Bug #32004 IN list select using DISTINCT Submitted: 31 Oct 2007 20:09Modified: 1 Dec 2007 10:17 Reporter: Bill McCaffrey Email Updates: Status: No Feedback Impact on me: None Category: MySQL Server: ParserSeverity: S1 (Critical) Version: 5.0.45-logOS: Linux Assigned to: CPU ...
--注释内容【--后必须有空格】#注释内容(mysql特有) 多行注释 /*注释*/ DDL:数据定义语言 用来定义数据库对象:数据库,表,列表。关键字:create,drop,alter DML:数据操作语言 用来对数据库中表的记录进行增删改。关键字:insert,delete,update DQL:数据查询语言 ...