MySQL数据库数据类型之集合类型SET测试总结
说明：
MySQL数据库提供针对字符串存储的一种特殊数据类型：集合类型SET，这种数据类型可以给予我们更多提高性能、降低存储容量和降低程序代码理解的技巧，前面介绍了首先介绍了四种数据类型的特性总结，其后又分别介绍了布尔类型BOOL或称布尔类型BOOLEAN、枚举类型ENUM。
本文详细介绍集合类型set测试过程与总结，加深对mysql数据库集合类型set的理解记忆。
n 集合类型 SET
a).数据库表mysqlops_set结构
执行创建数据库表mysqlops_set的语句：
-> Work_Option SET('','DBA','SA','Coding Engineer','JavaScript','NA','QA','other') NOT NULL,
-> Work_City SET('shanghai','beijing','hangzhou','shenzhen','guangzhou','other') NOT NULL DEFAULT 'shanghai',
-> PRIMARY KEY(ID)
-> )ENGINE=InnoDB CHARACTER SET 'utf8' COLLATE 'utf8_general_ci';
Query OK, 0 rows affected (0.00 sec)
查阅数据库中创建的mysqlops_set表的结构定义信息：
*************************** 1. row ***************************
Table: Mysqlops_set
Create Table: CREATE TABLE `Mysqlops_set` (
`ID` int(11) NOT NULL AUTO_INCREMENT,
`Work_Option` set('','DBA','SA','Coding Engineer','JavaScript','NA','QA','other') NOT NULL,
`Work_City` set('shanghai','beijing','hangzhou','shenzhen','guangzhou','other') NOT NULL DEFAULT 'shanghai',
PRIMARY KEY (`ID`)
) ENGINE=InnoDB AUTO_INCREMENT=10 DEFAULT CHARSET=utf8
1 row in set (0.00 sec)
小结：
对于集合类型字段定义，MySQL没有做任何强制性转换或修改。
b). 写入不同类型的测试数据
[root@jbxue] : test 05:06:19> INSERT INTO Mysqlops_SET(ID,Work_Option,Work_City) VALUES(1,'QA','shanghai');
Query OK, 1 row affected (0.00 sec)
[root@jbxue] : test 05:06:26> INSERT INTO Mysqlops_SET(ID,Work_Option,Work_City) VALUES(2,'NA','');
Query OK, 1 row affected (0.00 sec)
[root@jbxue] : test 05:06:33> INSERT INTO Mysqlops_SET(ID,Work_Option,Work_City) VALUES(3,'Other',NULL);
ERROR 1048 (23000): Column 'Work_City' cannot be null
[root@jbxue] : test 05:06:47> INSERT INTO Mysqlops_SET(ID,Work_Option,Work_City) VALUES(3,'','hangzhou');
Query OK, 1 row affected (0.00 sec)
[root@jbxue] : test 05:06:55> INSERT INTO Mysqlops_SET(ID,Work_City) VALUES(4,'ningbo');
Query OK, 1 row affected, 2 warnings (0.00 sec)
[root@jbxue] : test 05:07:09> SHOW WARNINGS;
+---------+------+--------------------------------------------------+
| Level | Code | Message |
+---------+------+--------------------------------------------------+
| Warning | 1364 | Field 'Work_Option' doesn't have a default value |
| Warning | 1265 | Data truncated for column 'Work_City' at row 1 |
+---------+------+--------------------------------------------------+
2 rows in set (0.00 sec)
[root@jbxue] : test 05:07:19> INSERT INTO Mysqlops_SET(ID,Work_Option) VALUES(5,'DBA');
Query OK, 1 row affected (0.00 sec)
[root@jbxue] : test 03:06:01> INSERT INTO Mysqlops_SET(ID,Work_Option,Work_City) VALUES(6,'DBA','shanghai');
Query OK, 1 row affected (0.00 sec)
[root@jbxue] : test 03:06:10> INSERT INTO Mysqlops_SET(ID,Work_Option,Work_City) VALUES(7,'DBA,SA','shanghai,beijing');
Query OK, 1 row affected (0.00 sec)
[root@jbxue] : test 03:06:18> INSERT INTO Mysqlops_SET(ID,Work_Option,Work_City) VALUES(8,'DBA,SA,NA','shanghai,beijing,hangzhou');
Query OK, 1 row affected (0.00 sec)
[root@jbxue] : test 03:06:12> INSERT INTO Mysqlops_SET(ID,Work_Option,Work_City) VALUES(9,'DBA,SA,NA','shanghai,beijing,hangzhou,shenzhen,guangzhou,other');
Query OK, 1 row affected (0.00 sec)
[root@jbxue] : test 03:18:25> INSERT INTO Mysqlops_SET(ID,Work_Option,Work_City) VALUES(20,'DBA,SA,NA','shanghai,beijing,hangzhou!shenzhen!guangzhou!other');
Query OK, 1 row affected, 1 warning (0.00 sec)
[root@jbxue] : test 03:18:27> show warnings;
+---------+------+------------------------------------------------+
| Level | Code | Message |
+---------+------+------------------------------------------------+
| Warning | 1265 | Data truncated for column 'Work_City' at row 1 |
+---------+------+------------------------------------------------+
1 row in set (0.00 sec)
小结：
集合类型SET字段即使没有定义空格字符串作为元素，也会默认成为其中一个组成元素；
集合类型SET字段不允许为NULL时，向其写入NULL值会报错，导致SQL执行失败；
集合类型SET字段不允许为NULL且无显式申明默认值时，未集合类型字段给出值的INSERT操作，会出现警告信息，提示字段值阶段，并且用空字符串值替代，SQL语句执行成功；
集合类型SET字段的值域列表中有空字符串元素时，决断用空字符串值替代的记录，与显式写入空字符串值的序列编号不同，前者序号为0，后者序号为值域列表中真实的顺序；
向集合类型SET字段写入一个值域列表中，不存在的值，会发生字段值截断，并且用空格字符串替代，SQL语句执行成功；
集合类型SET字段值域列表中任意元素的组合，只要用逗号分隔，就是合法的值；
集合类型SET字段值域列表中任意元素的组合时，若部分元素的值没有用逗号分隔，或者部分不是值域列表中元素值或组合，则会把非法的部分截断掉，并且给出警告信息，SQL语句执行成功；
c). 查询数据库表mysqlops_SET的数据
[root@jbxue] : test 03:18:31> select * from mysqlops_SET;
+----+-----------------+----------------------------------------------------+
| ID | Work_Option | Work_City |
+----+-----------------+----------------------------------------------------+
| 1 | QA | shanghai |
| 2 | NA ||
| 3 | | hangzhou |
| 4 | ||
| 5 | DBA | shanghai |
| 6 | DBA | shanghai |
| 7 | DBA,SA | shanghai,beijing |
| 8 | DBA,SA,NA | shanghai,beijing,hangzhou|
| 9 | DBA,SA,NA | shanghai,beijing,hangzhou,shenzhen,guangzhou,other |
| 10 | Coding Engineer ||
| 11 | Coding Engineer | shanghai |
| 12 | | shanghai |
| 13 | | hangzhou |
| 20 | DBA,SA,NA | shanghai,beijing |
+----+-----------------+----------------------------------------------------+
14 rows in set (0.00 sec)
[root@jbxue] : test 03:07:02> SELECT * FROM mysqlops_set WHERE Work_Option=0;
+----+-------------+-----------+
| ID | Work_Option | Work_City |
+----+-------------+-----------+
| 3 | | hangzhou |
| 4 | | |
+----+-------------+-----------+
2 rows in set (0.00 sec)
[root@jbxue] : test 03:07:42> SELECT * FROM mysqlops_set WHERE Work_Option=1;
Empty set (0.00 sec)
[root@jbxue] : test 03:07:44> SELECT * FROM mysqlops_set WHERE Work_Option=2;
+----+-------------+-----------+
| ID | Work_Option | Work_City |
+----+-------------+-----------+
| 5 | DBA | shanghai |
| 6 | DBA | shanghai |
+----+-------------+-----------+
2 rows in set (0.00 sec)
[root@jbxue] : test 03:08:09> SELECT * FROM mysqlops_set WHERE Work_Option=6;
+----+-------------+------------------+
| ID | Work_Option | Work_City |
+----+-------------+------------------+
| 7 | DBA,SA | shanghai,beijing |
+----+-------------+------------------+
1 row in set (0.00 sec)
[root@jbxue] : test 03:10:04> SELECT * FROM mysqlops_set WHERE Work_City=0;
+----+-------------+-----------+
| ID | Work_Option | Work_City |
+----+-------------+-----------+
| 2 | NA | |
| 4 | | |
+----+-------------+-----------+
2 rows in set (0.00 sec)
[root@jbxue] : test 03:10:18> SELECT * FROM mysqlops_set WHERE Work_City=1;
+----+-------------+-----------+
| ID | Work_Option | Work_City |
+----+-------------+-----------+
| 1 | QA | shanghai |
| 5 | DBA | shanghai |
| 6 | DBA | shanghai |
+----+-------------+-----------+
3 rows in set (0.00 sec)
[root@jbxue] : test 03:10:20> SELECT * FROM mysqlops_set WHERE Work_City=2;
Empty set (0.00 sec)
[root@jbxue] : test 03:10:22> SELECT * FROM mysqlops_set WHERE Work_City=3;
+----+-------------+------------------+
| ID | Work_Option | Work_City |
+----+-------------+------------------+
| 7 | DBA,SA | shanghai,beijing |
+----+-------------+------------------+
1 row in set (0.00 sec)
[root@jbxue] : test 03:10:24> SELECT * FROM mysqlops_set WHERE Work_City=4;
+----+-------------+-----------+
| ID | Work_Option | Work_City |
+----+-------------+-----------+
| 3 | | hangzhou |
+----+-------------+-----------+
1 row in set (0.00 sec)
[root@jbxue] : test 03:10:30> SELECT * FROM mysqlops_set WHERE Work_City=7;
+----+-------------+---------------------------+
| ID | Work_Option | Work_City |
+----+-------------+---------------------------+
| 8 | DBA,SA,NA | shanghai,beijing,hangzhou |
+----+-------------+---------------------------+
1 row in set (0.00 sec)
[root@jbxue] : test 03:13:13> SELECT * FROM mysqlops_set WHERE Work_City=63;
+----+-------------+----------------------------------------------------+
| ID | Work_Option | Work_City |
+----+-------------+----------------------------------------------------+
| 9 | DBA,SA,NA | shanghai,beijing,hangzhou,shenzhen,guangzhou,other |
+----+-------------+----------------------------------------------------+
1 row in set (0.00 sec)
集合类型SET元素的存储顺序梳理：
集合类型值域列表顺序
值域列表顺序对应的元素值
存储序号二进制编码
二进制编码对应的十进制值
1
shanghai
0000,0001
1
2
beijing
0000,0010
2
3
hangzhou
0000,0100
4
4
shenzhen
0000,1000
8
5
guangzhou
0001,0000
16
6
other
0010,0000
32
l 集合类型字段存储的值
自增序列字段的值
集合类型字段Work_City的值
二进制编码
十进制值
1
shanghai
0000,0001
1
2
空格字符串
0000,0000
0
3
hangzhou
0000,0100
4
4
空格字符串
0000,0000
0
5
shanghai
0000,0001
1
6
shanghai
0000,0001
1
7
Shanghai,beijing
0000,0011
3
8
shanghai,beijing,hangzhou
0000,0111
7
9
shanghai,beijing,hangzhou,shenzhen,guangzhou,other
0011,1111
63
10
空格字符串
0000,0000
0
11
shanghai
0000,0001
1
12
shanghai
0000,0001
1
13
hangzhou
0000,0100
4
20
shanghai,beijing
0000,0011
3
小结：
出现字段值截断警告提示信息的记录行，对应的字段值都是用空字符串替换掉，且存储序号为0；
若是集合类型SET字段列表中，元素列表中显式定义空字符串，其存储序列编号也为0；
通过根据存储序号查询出来的数据，与集合类型SET元素列表顺序、自增序列值大小对比，我们可以得出如下信息：
l 集合类型SET值域列表中，第一个元素的存储顺序编号为：0000,0001；
l 集合类型SET值域列表中，第一个元素之后的元素存储顺序编号为，前一个元素存储序号十进制值的二倍；
l 集合类型SET字段，若存储的数据是值域列表中的元素组合，则是每个元素存储顺序的值相加，则是对应组合值的存储顺序号；
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