(编辑：jimmy 日期: 2024/12/27 浏览：2)
mysql字符类型默认是不区分大小写的，即select * from t where name='AAA'与='aaa'没区别，以下是测试的例子
(root@localhost)[hello]> create table test1(id int, name varchar(10)); (root@localhost)[hello]> insert into test1 values(1,'aaa'),(2,'AAA'),(3,'bbb'),(4,'BbB'); (root@localhost)[hello]> select * from test1; +------+------+ | id | name | +------+------+ | 1 | aaa | | 2 | AAA | | 3 | bbb | | 4 | BbB | +------+------+ (root@localhost)[hello]> select * from test1 where name = 'AAA'; +------+------+ | id | name | +------+------+ | 1 | aaa | | 2 | AAA | +------+------+ (root@localhost)[hello]> select * from test1 where name = 'aaa'; +------+------+ | id | name | +------+------+ | 1 | aaa | | 2 | AAA | +------+------+
可以看到此时where条件后面的'AAA'与'aaa'，查出来的结果没啥区别。
如果只想找出'AAA'的可以有以下几种办法
1.在sql中加入binary关键字
(root@localhost)[hello]> select * from test1 where binary name = 'AAA'; +------+------+ | id | name | +------+------+ | 2 | AAA | +------+------+
2.修改列的定义
先查看原始表的定义
(root@localhost)[hello]> show create table test1\G *************************** 1. row *************************** Table: test1 Create Table: CREATE TABLE `test1` ( `id` int(11) DEFAULT NULL, `name` varchar(10) DEFAULT NULL ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4
修改表test1的name列
alter table test1 modify column name varchar(10) character set utf8mb4 collate utf8mb4_bin default null;
collate utf8mb4_bin表示where过滤或者order by排序区分大小写
此时查看test1的定义
(root@localhost)[hello]> show create table test1\G *************************** 1. row *************************** Table: test1 Create Table: CREATE TABLE `test1` ( `id` int(11) DEFAULT NULL, `name` varchar(10) CHARACTER SET utf8mb4 COLLATE utf8mb4_bin DEFAULT NULL ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4
接着再执行查询语句
(root@localhost)[hello]> select * from test1 where name='AAA'; +------+------+ | id | name | +------+------+ | 2 | AAA | +------+------+
下面再创建一张test2表，就会发现上面修改列的语句其实相当于在创建表时varchar后面跟binary
(root@localhost)[hello]> create table test2(id int, name varchar(10) binary); (root@localhost)[hello]> show create table test2\G *************************** 1. row *************************** Table: test2 Create Table: CREATE TABLE `test2` ( `id` int(11) DEFAULT NULL, `name` varchar(10) CHARACTER SET utf8mb4 COLLATE utf8mb4_bin DEFAULT NULL ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4
下面介绍如何设置字符大小写敏感
创建
create database <db_name> default character set utf8mb4 collate utf8mb4_bin;
修改
alter database <db_name> default character set utf8mb4 collate utf8mb4_bin;
创建
create table <tb_name> ( ...... ) engine=innodb default charset=utf8mb4 collate=utf8mb4_bin;
修改
alter table <tb_name> engine=innodb default charset=utf8mb4 collate=utf8mb4_bin;
创建
create table <tb_name> ( `field1` varchar(10) character set utf8mb4 collate utf8mb4_bin, ...... )
修改
alter table <tb_name> modify column `field1` varchar(10) character set utf8mb4 collate utf8mb4_bin default null;
继承关系是列-->表-->库，优先级是列>表>库
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