這篇文章給大家分享的是有關(guān)MySQL中BINARY怎么用的內(nèi)容。小編覺(jué)得挺實(shí)用的，因此分享給大家做個(gè)參考，一起跟隨小編過(guò)來(lái)看看吧。

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數(shù)據(jù)庫(kù)版本:
MySQL 5.6.26

線上某業(yè)務(wù)表為了區(qū)分大小寫(xiě)，使用BINARY關(guān)鍵字，正常來(lái)說(shuō)使用這個(gè)關(guān)鍵字是走索引的，測(cè)試過(guò)程如下：

創(chuàng)建測(cè)試表，插入數(shù)據(jù)：

drop table  if EXISTS student;

CREATE TABLE `student` (
  `id` int(11) PRIMARY key auto_increment,
  `name` varchar(20) DEFAULT NULL,
key `idx_name`(`name`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 ;

insert into `student` ( `id`, `name`) values ( '1', 'michael');
insert into `student` ( `id`, `name`) values ( '2', 'lucy');
insert into `student` ( `id`, `name`) values ( '3', 'nacy');
insert into `student` ( `id`, `name`) values ( '4', 'mike');
insert into `student` ( `id`, `name`) values ( null, 'guo');
insert into `student` ( `id`, `name`) values ( '6', 'Guo');
不加BINARY關(guān)鍵字可以走索引：

mysql> desc select * from student where name = 'guo';
+----+-------------+---------+------+---------------+----------+---------+-------+------+--------------------------+
| id | select_type | table   | type | possible_keys | key      | key_len | ref   | rows | Extra                    |
+----+-------------+---------+------+---------------+----------+---------+-------+------+--------------------------+
| 1  | SIMPLE      | student | ref  | idx_name      | idx_name | 63      | const | 2    | Using where; Using index |
+----+-------------+---------+------+---------------+----------+---------+-------+------+--------------------------+
1 rows in set (0.03 sec)
正常來(lái)說(shuō)BINARY關(guān)鍵字是可以走索引的：

mysql> desc select * from student where BINARY name = 'guo';
+----+-------------+---------+-------+---------------+----------+---------+------+------+--------------------------+
| id | select_type | table   | type  | possible_keys | key      | key_len | ref  | rows | Extra                    |
+----+-------------+---------+-------+---------------+----------+---------+------+------+--------------------------+
| 1  | SIMPLE      | student | index | NULL          | idx_name | 63      | NULL | 6    | Using where; Using index |
+----+-------------+---------+-------+---------------+----------+---------+------+------+--------------------------+
1 rows in set (0.04 sec)
不使用BINARY關(guān)鍵字默認(rèn)不會(huì)區(qū)分大小寫(xiě)：

mysql> select * from student where name = 'guo';
+----+------+
| id | name |
+----+------+
| 5  | guo  |
| 6  | Guo  |
+----+------+
2 rows in set (0.03 sec)

mysql> select * from student where name = 'Guo';
+----+------+
| id | name |
+----+------+
| 5  | guo  |
| 6  | Guo  |
+----+------+
2 rows in set (0.03 sec)
使用BINARY關(guān)鍵字可以區(qū)分大小寫(xiě)：

mysql>  select * from student where BINARY name = 'guo';
+----+------+
| id | name |
+----+------+
| 5  | guo  |
+----+------+
1 rows in set (0.04 sec)

mysql>  select * from student where BINARY name = 'Guo';
+----+------+
| id | name |
+----+------+
| 6  | Guo  |
+----+------+
1 rows in set (0.03 sec)

mysql>
到這里以上都沒(méi)問(wèn)題，但關(guān)鍵在于，業(yè)務(wù)的表結(jié)構(gòu)大于索引的最大長(zhǎng)度即字串長(zhǎng)度超過(guò)255。

CREATE TABLE `student` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(2000) DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `idx_name` (`name`(255))
) ENGINE=InnoDB AUTO_INCREMENT=7 DEFAULT CHARSET=utf8

mysql> desc select * from student where name = 'guo';
+----+-------------+---------+------+---------------+----------+---------+-------+------+-------------+
| id | select_type | table   | type | possible_keys | key      | key_len | ref   | rows | Extra       |
+----+-------------+---------+------+---------------+----------+---------+-------+------+-------------+
| 1  | SIMPLE      | student | ref  | idx_name      | idx_name | 768     | const | 2    | Using where |
+----+-------------+---------+------+---------------+----------+---------+-------+------+-------------+
1 rows in set (0.04 sec)
加上BINARY關(guān)鍵字不再走索引：

mysql> desc select * from student where BINARY name = 'guo';
+----+-------------+---------+------+---------------+------+---------+------+------+-------------+
| id | select_type | table   | type | possible_keys | key  | key_len | ref  | rows | Extra       |
+----+-------------+---------+------+---------------+------+---------+------+------+-------------+
| 1  | SIMPLE      | student | ALL  | NULL          | NULL | NULL    | NULL | 6    | Using where |
+----+-------------+---------+------+---------------+------+---------+------+------+-------------+
1 rows in set (0.05 sec)

mysql>
這時(shí)需要在表結(jié)構(gòu)里加上BINARY

mysql>ALTER TABLE student MODIFY COLUMN name VARCHAR(20) BINARY;
Query OK, 6 rows affected (0.06 sec)
數(shù)據(jù)庫(kù)會(huì)自動(dòng)轉(zhuǎn)換成COLLATE utf8_bin
collate關(guān)鍵字為校對(duì)集，主要是對(duì)字符集之間的比較和排序，可以通過(guò) show collation查看所有的校對(duì)集

mysql> show create table student\G
*************************** 1. row ***************************
Table       : student
Create Table: CREATE TABLE `student` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(20) CHARACTER SET utf8 COLLATE utf8_bin DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `idx_name` (`name`)
) ENGINE=InnoDB AUTO_INCREMENT=7 DEFAULT CHARSET=utf8
1 rows in set (0.39 sec)

mysql>


mysql> desc select * from student where name = 'guo';
+----+-------------+---------+------+---------------+----------+---------+-------+------+--------------------------+
| id | select_type | table   | type | possible_keys | key      | key_len | ref   | rows | Extra                    |
+----+-------------+---------+------+---------------+----------+---------+-------+------+--------------------------+
| 1  | SIMPLE      | student | ref  | idx_name      | idx_name | 63      | const | 1    | Using where; Using index |
+----+-------------+---------+------+---------------+----------+---------+-------+------+--------------------------+
1 rows in set (0.07 sec)

mysql>
即可區(qū)分大小寫(xiě)：

mysql> select * from student where name = 'guo';
+----+------+
| id | name |
+----+------+
| 5  | guo  |
+----+------+
1 rows in set (0.07 sec)

mysql> select * from student where name = 'Guo';
+----+------+
| id | name |
+----+------+
| 6  | Guo  |
+----+------+
1 rows in set (0.06 sec)

mysql>

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