alter table 表名 add 列名 类型 primary key [auto_increment]; 1. 举例: mysql> create table t11(name char(11)); Query OK, 0 rows affected (0.02 sec) mysql> alter table t11 add id int primary key auto_increment first; Query OK, 0 rows affected (0.05 sec) Records: 0 Duplicates: 0 ...
一、索引 索引在MySQL中也叫‘键’或者‘key’,是存储引擎用于快速找到记录的一种数据结构。索引对于良好的性能非常关键,尤其是当表中的数据量越来越大时,索引对于性能的影响愈发重要,减少IO次数,加快查询。 索引的数据类型是b+树,要想理解b+树,最好先依次理解二叉树、平衡二叉树就比较好理解b+树了,所以索引查...
By going through step by step in this tutorial, we will see the basic difference betweenPRI,MUL, andUNIkeys and how to use each of them. We will also see their effect in the table using the example code. Keys in MySQL The key is an attribute or sometimes a set of attributes used to...
1. 如果Key是PRI, 那么该列是主键的组成部分 2. 如果Key是UNI, 那么该列是一个唯一值索引的第一列(前导列),并别不能含有空值(NULL)3. 如果Key是MUL, 那么该列的值可以重复, 该列是一个非唯一索引的前导列(第一列)或者是一个唯一性索引的组成部分但是可以含有空值NULL ...
MySQL Key值(PRI, UNI, MUL)的含义 PRI主键约束; UNI唯一约束; MUL可以重复。 参考:http://www.codebit.cn/mysql/deleting-duplicate-rows-in-a-mysql-database.html
CREATE TABLE users ( id INT PRIMARY KEY, name VARCHAR(50), age INT, city VARCHAR(50) ); CREATE INDEX idx_name_city ON users(name, city); 参考链接 MySQL官方文档 - 多列索引 常见问题及解决方法 为什么Mul索引没有生效? 原因:可能是查询条件没有使用到索引列,或者使用了函数、计算表达式等导致索引...
I have looked everywhere for answers! I am fairly new to MySQL and am trying to remove the MUL key from the starttime and endtime fields in my database...
MySQL Forums Forum List»Newbie What is "MUL? Posted by:Tara Wilk Date: March 14, 2008 06:58AM When I specify a FOREIGN KEY constraint, and then do a "desc" on that table, the Foreign Key row displays "MUL" in the Key Column. What is that?
(COUNTRY_CODE), #this is MUL Key CITIZEN_ID INT UNIQUE KEY #this is UNI Key ); #insert some data INSERT INTO employee(ID, FIRST_NAME, LAST_NAME,GENDER, COUNTRY_CODE,CITIZEN_ID) VALUES (1,'Thomas', 'Christopher','Male','+61',485), (2,'Lisa', 'Mark', 'Female','+59',408)...
This was moved over to the Newbie Forum (titled, MUL), but in any case, turns out its a bug. http://bugs.mysql.com/bug.php?id=11227Navigate: Previous Message• Next Message Options: Reply• Quote Subject Written By Posted unique_key vs MUL Keith D Commiskey May 08, 2006 03:...