mysql字符類型默認是不區(qū)分大小寫的，即select * from t where name='AAA'與='aaa'沒區(qū)別，以下是測試的例子
(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 | +------+------+
可以看到此時where條件后面的'AAA'與'aaa'，查出來的結果沒啥區(qū)別。
如果只想找出'AAA'的可以有以下幾種辦法
1.在sql中加入binary關鍵字
(root@localhost)[hello]> select * from test1 where binary name = 'AAA'; +------+------+ | id | name | +------+------+ | 2 | AAA | +------+------+
2.修改列的定義
先查看原始表的定義
(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過濾或者order by排序區(qū)分大小寫
此時查看test1的定義
(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
接著再執(zhí)行查詢語句
(root@localhost)[hello]> select * from test1 where name='AAA'; +------+------+ | id | name | +------+------+ | 2 | AAA | +------+------+
下面再創(chuàng)建一張test2表，就會發(fā)現上面修改列的語句其實相當于在創(chuàng)建表時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
下面介紹如何設置字符大小寫敏感
創(chuàng)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;
創(chuàng)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;
創(chuàng)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;
繼承關系是列-->表-->庫，優(yōu)先級是列>表>庫
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