MySQL中BINARY怎么用

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數據庫版本:
MySQL 5.6.26

線上某業務表為了區分大小寫，使用BINARY關鍵字，正常來說使用這個關鍵字是走索引的，測試過程如下：

創建測試表，插入數據：

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)
正常來說BINARY關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關鍵字默認不會區分大小寫：

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關鍵字可以區分大小寫：

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>
到這里以上都沒問題，但關鍵在于，業務的表結構大于索引的最大長度即字串長度超過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>
這時需要在表結構里加上BINARY

mysql>ALTER TABLE student MODIFY COLUMN name VARCHAR(20) BINARY;
Query OK, 6 rows affected (0.06 sec)
數據庫會自動轉換成COLLATE utf8_bin
collate關鍵字為校對集，主要是對字符集之間的比較和排序，可以通過 show collation查看所有的校對集

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>
即可區分大小寫：

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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