SpringBoot-14-MyBatis预热篇，MySQL小结

1.在总结MyBatis之前，还是先巩固一下MySQL的知识吧，毕竟MyBatis是SQL语句为王。
2.为了后面有素材可以实验，借此弄个库也不错。
3.如果你觉得自己MySQL很厉害，只是想看MyBatis，可以看一下表结构,不必细究。

创建一张剑的表，并显示表信息：

剑表：id，名称，攻击，命中，暴击

CREATE TABLE sword (
id SMALLINT UNSIGNED AUTO_INCREMENT PRIMARY KEY,
name VARCHAR(32) NOT NULL,
atk SMALLINT UNSIGNED NOT NULL,
hit SMALLINT UNSIGNED NOT NULL DEFAULT 20,
crit SMALLINT UNSIGNED NOT NULL DEFAULT 10
); 
Query OK, 0 rows affected (0.39 sec)

mysql> DESC sword;
+-------+----------------------+------+-----+---------+-------+
| Field | Type                 | Null | Key | Default | Extra |
+-------+----------------------+------+-----+---------+-------+
| id    | smallint(5) unsigned | NO   | PRI | NULL    |       |
| name  | varchar(32)          | NO   |     | NULL    |       |
| atk   | smallint(5) unsigned | NO   |     | NULL    |       |
| hit   | smallint(5) unsigned | NO   |     | NULL    |       |
| crit  | smallint(5) unsigned | NO   |     | NULL    |       |
+-------+----------------------+------+-----+---------+-------+
5 rows in set (0.01 sec)

插入：INSERT

插入两条数据，id会自递加，id位可用DEFAULT或NULL

mysql> INSERT sword VALUES(NULL,'黑风',10000,400,400);
Query OK, 1 row affected (0.00 sec)

mysql> SELECT*FROM sword;
+----+--------+-------+-----+------+
| id | name   | atk   | hit | crit |
+----+--------+-------+-----+------+
|  1 | 黑风   | 10000 | 400 |  400 |
+----+--------+-------+-----+------+
1 row in set (0.01 sec)

mysql> INSERT sword VALUES(DEFAULT,'木藜',5000,200,200);
Query OK, 1 row affected (0.01 sec)

mysql> SELECT*FROM sword;
+----+--------+-------+-----+------+
| id | name   | atk   | hit | crit |
+----+--------+-------+-----+------+
|  1 | 黑风   | 10000 | 400 |  400 |
|  2 | 木藜   |  5000 | 200 |  200 |
+----+--------+-------+-----+------+
2 rows in set (0.00 sec)

有DEFAULT的字段，赋值时用DEFAULT则会插入默认值

复习一下修改字段信息

mysql> ALTER TABLE sword MODIFY crit SMALLINT UNSIGNED DEFAULT 10;
Query OK, 0 rows affected (0.05 sec)
Records: 0  Duplicates: 0  Warnings: 0
mysql> DESC sword;
+-------+----------------------+------+-----+---------+----------------+
| Field | Type                 | Null | Key | Default | Extra          |
+-------+----------------------+------+-----+---------+----------------+
| id    | smallint(5) unsigned | NO   | PRI | NULL    | auto_increment |
| name  | varchar(32)          | NO   |     | NULL    |                |
| atk   | smallint(5) unsigned | NO   |     | NULL    |                |
| hit   | smallint(5) unsigned | NO   |     | NULL    |                |
| crit  | smallint(5) unsigned | YES  |     | 10      |                |
+-------+----------------------+------+-----+---------+----------------+
5 rows in set (0.00 sec)
mysql> INSERT sword VALUES(DEFAULT,'荆戈',8000,1000,DEFAULT);
Query OK, 1 row affected (0.00 sec)

mysql> SELECT*FROM sword;
+----+--------+-------+------+------+
| id | name   | atk   | hit  | crit |
+----+--------+-------+------+------+
|  1 | 黑风   | 10000 |  400 |  400 |
|  2 | 木藜   |  5000 |  200 |  200 |
|  3 | 荆戈   |  8000 | 1000 |   10 |
+----+--------+-------+------+------+
3 rows in set (0.00 sec)

一次插入多行，逗号隔开

mysql> INSERT sword VALUES(
    -> DEFAULT,'痕兮',7000,800,999),
    -> (DEFAULT,'逐暮',100,1000,10000),
    -> (DEFAULT,'风跃',9000,10,DEFAULT
    -> );
Query OK, 3 rows affected (0.00 sec)
Records: 3  Duplicates: 0  Warnings: 0

mysql> SELECT*FROM sword;
+----+--------+-------+------+-------+
| id | name   | atk   | hit  | crit  |
+----+--------+-------+------+-------+
|  1 | 黑风   | 10000 |  400 |   400 |
|  2 | 木藜   |  5000 |  200 |   200 |
|  3 | 荆戈   |  8000 | 1000 |    10 |
|  4 | 痕兮   |  7000 |  800 |   999 |
|  5 | 逐暮   |   100 | 1000 | 10000 |
|  6 | 风跃   |  9000 |   10 |    10 |
+----+--------+-------+------+-------+
6 rows in set (0.00 sec)

有把剑不想让人知道名字，这里用MD5加密

mysql> INSERT sword VALUES(DEFAULT,MD5('隐锋'),8000,2000,10);
Query OK, 1 row affected (0.00 sec)

mysql> SELECT*FROM sword;
+----+----------------------------------+-------+------+-------+
| id | name                             | atk   | hit  | crit  |
+----+----------------------------------+-------+------+-------+
|  1 | 黑风                             | 10000 |  400 |   400 |
|  2 | 木藜                             |  5000 |  200 |   200 |
|  3 | 荆戈                             |  8000 | 1000 |    10 |
|  4 | 痕兮                             |  7000 |  800 |   999 |
|  5 | 逐暮                             |   100 | 1000 | 10000 |
|  6 | 风跃                             |  9000 |   10 |    10 |
|  7 | 99f3a83768bb97bc7644f0ee278897dc |  8000 | 2000 |    10 |
+----+----------------------------------+-------+------+-------+
7 rows in set (0.00 sec)

用另一种方式插入值

mysql> INSERT sword SET name='洛神',atk='20000',hit=1;
Query OK, 1 row affected (0.01 sec)

mysql> SELECT*FROM sword;
+----+----------------------------------+-------+------+-------+
| id | name                             | atk   | hit  | crit  |
+----+----------------------------------+-------+------+-------+
|  1 | 黑风                             | 10000 |  400 |   400 |
|  2 | 木藜                             |  5000 |  200 |   200 |
|  3 | 荆戈                             |  8000 | 1000 |    10 |
|  4 | 痕兮                             |  7000 |  800 |   999 |
|  5 | 逐暮                             |   100 | 1000 | 10000 |
|  6 | 风跃                             |  9000 |   10 |    10 |
|  7 | 99f3a83768bb97bc7644f0ee278897dc |  8000 | 2000 |    10 |
|  8 | 洛神                             | 20000 |    1 |    10 |
+----+----------------------------------+-------+------+-------+
8 rows in set (0.00 sec)

第三种方法插入数据

新建一个测试表：将sword_insert_test中test_name赋值为sword表中id大于5的name

mysql> CREATE TABLE sword_insert_test (
    -> id SMALLINT UNSIGNED AUTO_INCREMENT PRIMARY KEY,
    -> test_name VARCHAR(32) NOT NULL
    -> );
Query OK, 0 rows affected (0.05 sec)
mysql> SELECT*FROM sword_insert_test ;
Empty set (0.01 sec)
mysql> INSERT sword_insert_test(test_name) SELECT name FROM sword WHERE id>5;
Query OK, 3 rows affected (0.00 sec)
Records: 3  Duplicates: 0  Warnings: 0

mysql> SELECT*FROM sword_insert_test ;
+----+-----------+
| id | test_name |
+----+-----------+
|  1 | 风跃      |
|  2 | 洛神      |
|  3 | 隐锋      |
+----+-----------+
3 rows in set (0.00 sec)

更新数据UPDATE

更新某项值：将命中值(hit)全加1

mysql> UPDATE sword SET hit=hit+1;
Query OK, 8 rows affected (0.04 sec)
Rows matched: 8  Changed: 8  Warnings: 0

mysql> SELECT*FROM sword;
+----+----------------------------------+-------+------+-------+
| id | name                             | atk   | hit  | crit  |
+----+----------------------------------+-------+------+-------+
|  1 | 黑风                             | 10000 |  401 |   400 |
|  2 | 木藜                             |  5000 |  201 |   200 |
|  3 | 荆戈                             |  8000 | 1001 |    10 |
|  4 | 痕兮                             |  7000 |  801 |   999 |
|  5 | 逐暮                             |   100 | 1001 | 10000 |
|  6 | 风跃                             |  9000 |   11 |    10 |
|  7 | 99f3a83768bb97bc7644f0ee278897dc |  8000 | 2001 |    10 |
|  8 | 洛神                             | 20000 |    2 |    10 |
+----+----------------------------------+-------+------+-------+
8 rows in set (0.00 sec)

更新多项值：将攻击(atk)值修改为：攻击+暴击(crit)*2；命中全部减1；

mysql> UPDATE sword SET atk=atk+2*crit,hit=hit-1;
Query OK, 8 rows affected (0.00 sec)
Rows matched: 8  Changed: 8  Warnings: 0

mysql> SELECT*FROM sword;
+----+----------------------------------+-------+------+-------+
| id | name                             | atk   | hit  | crit  |
+----+----------------------------------+-------+------+-------+
|  1 | 黑风                             | 10800 |  400 |   400 |
|  2 | 木藜                             |  5400 |  200 |   200 |
|  3 | 荆戈                             |  8020 | 1000 |    10 |
|  4 | 痕兮                             |  8998 |  800 |   999 |
|  5 | 逐暮                             | 20100 | 1000 | 10000 |
|  6 | 风跃                             |  9020 |   10 |    10 |
|  7 | 99f3a83768bb97bc7644f0ee278897dc |  8020 | 2000 |    10 |
|  8 | 洛神                             | 20020 |    1 |    10 |
+----+----------------------------------+-------+------+-------+
8 rows in set (0.00 sec)

逐暮的属性太高了，下面来用限定条件对单条数据进行更新：

mysql> UPDATE sword SET atk=atk-20000 WHERE name='逐暮';
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> SELECT*FROM sword;
+----+----------------------------------+-------+------+-------+
| id | name                             | atk   | hit  | crit  |
+----+----------------------------------+-------+------+-------+
|  1 | 黑风                             | 10800 |  400 |   400 |
|  2 | 木藜                             |  5400 |  200 |   200 |
|  3 | 荆戈                             |  8020 | 1000 |    10 |
|  4 | 痕兮                             |  8998 |  800 |   999 |
|  5 | 逐暮                             |   100 | 1000 | 10000 |
|  6 | 风跃                             |  9020 |   10 |    10 |
|  7 | 99f3a83768bb97bc7644f0ee278897dc |  8020 | 2000 |    10 |
|  8 | 洛神                             | 20020 |    1 |    10 |
+----+----------------------------------+-------+------+-------+
8 rows in set (0.00 sec)

删除DELETE

第七个看着不舒服，删掉吧：

再插入没加密的：(注意，删掉id为7的，不会影响其他数据的id，再插入id为9)

mysql> DELETE FROM sword WHERE id=7;
Query OK, 1 row affected (0.07 sec)

mysql> SELECT*FROM sword;
+----+--------+-------+------+-------+
| id | name   | atk   | hit  | crit  |
+----+--------+-------+------+-------+
|  1 | 黑风   | 10800 |  400 |   400 |
|  2 | 木藜   |  5400 |  200 |   200 |
|  3 | 荆戈   |  8020 | 1000 |    10 |
|  4 | 痕兮   |  8998 |  800 |   999 |
|  5 | 逐暮   |   100 | 1000 | 10000 |
|  6 | 风跃   |  9020 |   10 |    10 |
|  8 | 洛神   | 20020 |    1 |    10 |
+----+--------+-------+------+-------+
7 rows in set (0.00 sec)
mysql> INSERT sword SET name='隐锋',atk=8020,hit=2000;
Query OK, 1 row affected (0.01 sec)

mysql> SELECT*FROM sword;
+----+--------+-------+------+-------+
| id | name   | atk   | hit  | crit  |
+----+--------+-------+------+-------+
|  1 | 黑风   | 10800 |  400 |   400 |
|  2 | 木藜   |  5400 |  200 |   200 |
|  3 | 荆戈   |  8020 | 1000 |    10 |
|  4 | 痕兮   |  8998 |  800 |   999 |
|  5 | 逐暮   |   100 | 1000 | 10000 |
|  6 | 风跃   |  9020 |   10 |    10 |
|  8 | 洛神   | 20020 |    1 |    10 |
|  9 | 隐锋   |  8020 | 2000 |    10 |
+----+--------+-------+------+-------+
8 rows in set (0.00 sec)

查询任何查询都不会影响表中的数据,)

查询指定字段：以id和name为例

mysql> SELECT id,name FROM sword;
+----+--------+
| id | name   |
+----+--------+
|  1 | 黑风   |
|  2 | 木藜   |
|  3 | 荆戈   |
|  4 | 痕兮   |
|  5 | 逐暮   |
|  6 | 风跃   |
|  8 | 洛神   |
|  9 | 隐锋   |
+----+--------+
8 rows in set (0.05 sec)

查询另一种方式

mysql> SELECT sword.id,sword.name FROM sword;
+----+--------+
| id | name   |
+----+--------+
|  1 | 黑风   |
|  2 | 木藜   |
|  3 | 荆戈   |
|  4 | 痕兮   |
|  5 | 逐暮   |
|  6 | 风跃   |
|  8 | 洛神   |
|  9 | 隐锋   |
+----+--------+
8 rows in set (0.00 sec)

为查询的字段取别名

mysql> SELECT crit AS '暴击',name AS'名称' FROM sword;
+--------+--------+
| 暴击   | 名称   |
+--------+--------+
|    400 | 黑风   |
|    200 | 木藜   |
|     10 | 荆戈   |
|    999 | 痕兮   |
|  10000 | 逐暮   |
|     10 | 风跃   |
|     10 | 洛神   |
|     10 | 隐锋   |
+--------+--------+
8 rows in set (0.00 sec)

查询指定位置的记录

查询指定位置的记录

分组

mysql> SELECT crit FROM sword GROUP BY crit;
+-------+
| crit  |
+-------+
|    10 |
|   200 |
|   400 |
|   999 |
| 10000 |
+-------+
5 rows in set (0.00 sec)

添加条件下的分组查询：

mysql> SELECT crit FROM sword GROUP BY crit HAVING crit<500;
+------+
| crit |
+------+
|   10 |
|  200 |
|  400 |
+------+
3 rows in set (0.01 sec)

降序排列

mysql> SELECT * FROM sword ORDER BY id DESC;
+----+--------+-------+------+-------+
| id | name   | atk   | hit  | crit  |
+----+--------+-------+------+-------+
|  9 | 隐锋   |  8020 | 2000 |    10 |
|  8 | 洛神   | 20020 |    1 |    10 |
|  6 | 风跃   |  9020 |   10 |    10 |
|  5 | 逐暮   |   100 | 1000 | 10000 |
|  4 | 痕兮   |  8998 |  800 |   999 |
|  3 | 荆戈   |  8020 | 1000 |    10 |
|  2 | 木藜   |  5400 |  200 |   200 |
|  1 | 黑风   | 10800 |  400 |   400 |
+----+--------+-------+------+-------+
8 rows in set (0.00 sec)

多条记录排序(当第一个字段相同，相同的数据按第二个字段再排)

mysql> SELECT * FROM sword ORDER BY crit,id DESC;
+----+--------+-------+------+-------+
| id | name   | atk   | hit  | crit  |
+----+--------+-------+------+-------+
|  9 | 隐锋   |  8020 | 2000 |    10 |
|  8 | 洛神   | 20020 |    1 |    10 |
|  6 | 风跃   |  9020 |   10 |    10 |
|  3 | 荆戈   |  8020 | 1000 |    10 |
|  2 | 木藜   |  5400 |  200 |   200 |
|  1 | 黑风   | 10800 |  400 |   400 |
|  4 | 痕兮   |  8998 |  800 |   999 |
|  5 | 逐暮   |   100 | 1000 | 10000 |
+----+--------+-------+------+-------+
8 rows in set (0.00 sec)

限制：LIMIT

查询前四条数据：

mysql> SELECT * FROM sword LIMIT 4;
+----+--------+-------+------+------+
| id | name   | atk   | hit  | crit |
+----+--------+-------+------+------+
|  1 | 黑风   | 10800 |  400 |  400 |
|  2 | 木藜   |  5400 |  200 |  200 |
|  3 | 荆戈   |  8020 | 1000 |   10 |
|  4 | 痕兮   |  8998 |  800 |  999 |
+----+--------+-------+------+------+
4 rows in set (0.00 sec)

查询前2~4条数据：

mysql> SELECT * FROM sword LIMIT 1,4;
+----+--------+------+------+-------+
| id | name   | atk  | hit  | crit  |
+----+--------+------+------+-------+
|  2 | 木藜   | 5400 |  200 |   200 |
|  3 | 荆戈   | 8020 | 1000 |    10 |
|  4 | 痕兮   | 8998 |  800 |   999 |
|  5 | 逐暮   |  100 | 1000 | 10000 |
+----+--------+------+------+-------+
4 rows in set (0.00 sec)

0准备工作：

先为剑表添加两个属性：属性(attr)和类型(type)

mysql> ALTER TABLE sword ADD attr VARCHAR(4) NOT NULL;
Query OK, 0 rows affected (0.11 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> ALTER TABLE sword ADD type VARCHAR(8) NOT NULL;
Query OK, 0 rows affected (0.08 sec)
Records: 0  Duplicates: 0  Warnings: 0
mysql> SELECT*FROM sword;
+----+--------+-------+------+-------+------+------+
| id | name   | atk   | hit  | crit  | attr | type |
+----+--------+-------+------+-------+------+------+
|  1 | 黑风   | 10800 |  400 |   400 |      |      |
|  2 | 木藜   |  5400 |  200 |   200 |      |      |
|  3 | 荆戈   |  8020 | 1000 |    10 |      |      |
|  4 | 痕兮   |  8998 |  800 |   999 |      |      |
|  5 | 逐暮   |   100 | 1000 | 10000 |      |      |
|  6 | 风跃   |  9020 |   10 |    10 |      |      |
|  8 | 洛神   | 20020 |    1 |    10 |      |      |
|  9 | 隐锋   |  8020 | 2000 |    10 |      |      |
+----+--------+-------+------+-------+------+------+
8 rows in set (0.00 sec)

修改数据：(为属性添加值)

mysql> UPDATE sword SET attr='木',type='神界' WHERE name='黑风';
Query OK, 0 rows affected (0.00 sec)
Rows matched: 1  Changed: 0  Warnings: 0

mysql> UPDATE sword SET attr='木',type='人界' WHERE name='木藜';
Query OK, 0 rows affected (0.01 sec)
Rows matched: 1  Changed: 0  Warnings: 0

mysql> UPDATE sword SET attr='金',type='魔界' WHERE name='荆戈';
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> UPDATE sword SET attr='水',type='道界' WHERE name='痕兮';
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> UPDATE sword SET attr='火',type='鬼界' WHERE name='逐暮';
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> UPDATE sword SET attr='木',type='仙界' WHERE name='风跃';
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> UPDATE sword SET attr='金',type='神界' WHERE name='洛神';
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> UPDATE sword SET attr='土',type='人界' WHERE name='隐锋';
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> SELECT*FROM sword;
+----+--------+-------+------+-------+------+--------+
| id | name   | atk   | hit  | crit  | attr | type   |
+----+--------+-------+------+-------+------+--------+
|  1 | 黑风   | 10800 |  400 |   400 | 木   | 神界   |
|  2 | 木藜   |  5400 |  200 |   200 | 木   | 人界   |
|  3 | 荆戈   |  8020 | 1000 |    10 | 金   | 魔界   |
|  4 | 痕兮   |  8998 |  800 |   999 | 水   | 道界   |
|  5 | 逐暮   |   100 | 1000 | 10000 | 火   | 鬼界   |
|  6 | 风跃   |  9020 |   10 |    10 | 木   | 仙界   |
|  8 | 洛神   | 20020 |    1 |    10 | 金   | 神界   |
|  9 | 隐锋   |  8020 | 2000 |    10 | 土   | 人界   |
+----+--------+-------+------+-------+------+--------+
8 rows in set (0.00 sec)
8 rows in set (0.00 sec)

子查询

出现在其他SQL语句内的SELECT语句
子查询必须在()内
增删改查都可以进行子查询
返回：标量，行，列或子查询

1.比较运算符的子查询(=、>、<、>=、<=、<>、!=、<=>)

• 计算平均攻击力(四舍五入2位)

mysql> SELECT ROUND(AVG(atk),2) AS '平均攻击力' FROM sword;
+-----------------+
| 平均攻击力      |
+-----------------+
|         8797.25 |
+-----------------+
1 row

• 普通查询：所有攻击力大于平均攻击力的剑，并降序排序

mysql> SELECT * FROM sword WHERE atk > 5636.36 ORDER BY atk DESC;
+----+--------+-------+------+------+------+--------+
| id | name   | atk   | hit  | crit | attr | type   |
+----+--------+-------+------+------+------+--------+
|  8 | 洛神   | 20020 |    1 |   10 | 金   | 神界   |
|  1 | 黑风   | 10800 |  400 |  400 | 木   | 神界   |
|  6 | 风跃   |  9020 |   10 |   10 | 木   | 仙界   |
|  4 | 痕兮   |  8998 |  800 |  999 | 水   | 道界   |
|  3 | 荆戈   |  8020 | 1000 |   10 | 金   | 魔界   |
|  9 | 隐锋   |  8020 | 2000 |   10 | 土   | 人界   |
+----+--------+-------+------+------+------+--------+
6 rows in set (0.00 sec)

• 使用子查询(也就是将上面两步简化为一步)

mysql> SELECT * FROM sword WHERE atk >
    -> (SELECT ROUND(AVG(atk),2) AS '平均攻击力' FROM sword)
    -> ORDER BY atk DESC;
+----+--------+-------+-----+------+------+--------+
| id | name   | atk   | hit | crit | attr | type   |
+----+--------+-------+-----+------+------+--------+
|  8 | 洛神   | 20020 |   1 |   10 | 金   | 神界   |
|  1 | 黑风   | 10800 | 400 |  400 | 木   | 神界   |
|  6 | 风跃   |  9020 |  10 |   10 | 木   | 仙界   |
|  4 | 痕兮   |  8998 | 800 |  999 | 水   | 道界   |
+----+--------+-------+-----+------+------+--------+
4 rows in set (0.00 sec)

2.ANY、SOME、ALL、IN

ANY     满足一条即可查询到
SOME    同ANY
ALL     满足所有可查询到
IN      等价于  = ANY 或 = SOME 

查询类型为人界的剑攻击力

mysql> SELECT atk FROM sword WHERE type = '人界';
+------+
| atk  |
+------+
| 5400 |
| 8020 |
+------+
2 rows in set (0.00 sec)
2 rows in set (0.00 sec)

查询攻击力大于(任意一个：ANY)"人族"的剑名称，并降序排列

虽然荆戈的攻击力不大于8020，但大于5400，满足一个就能查询到

mysql> SELECT id,name,atk FROM sword WHERE atk >
    -> ANY(SELECT atk FROM sword WHERE type = '人界')
    -> ORDER BY atk DESC;
+----+--------+-------+
| id | name   | atk   |
+----+--------+-------+
|  8 | 洛神   | 20020 |
|  1 | 黑风   | 10800 |
|  6 | 风跃   |  9020 |
|  4 | 痕兮   |  8998 |
|  3 | 荆戈   |  8020 |
|  9 | 隐锋   |  8020 |
+----+--------+-------+
6 rows in set (0.00 sec)

查询攻击力大于(所有：ALL)"人族"的剑名称，并降序排列

虽然荆戈的攻击力大于5400，但不大于8020，所以查不到

mysql> SELECT id,name,atk FROM sword WHERE atk >
    -> ALL(SELECT atk FROM sword WHERE type = '人界')
    -> ORDER BY atk DESC;
+----+--------+-------+
| id | name   | atk   |
+----+--------+-------+
|  8 | 洛神   | 20020 |
|  1 | 黑风   | 10800 |
|  6 | 风跃   |  9020 |
|  4 | 痕兮   |  8998 |
+----+--------+-------+
4 rows in set (0.00 sec)

查询任意攻击力等于"人族"的剑名称，并降序排列

mysql> SELECT id,name,atk FROM sword WHERE atk IN
    -> (SELECT atk FROM sword WHERE type = '人界')
    -> ORDER BY atk DESC;
+----+--------+------+
| id | name   | atk  |
+----+--------+------+
|  3 | 荆戈   | 8020 |
|  9 | 隐锋   | 8020 |
|  2 | 木藜   | 5400 |
+----+--------+------+
3 rows in set (0.00 sec)

创建类型分类表

• 建表

mysql> CREATE TABLE IF NOT EXISTS sword_type(
    -> type_id SMALLINT UNSIGNED PRIMARY KEY AUTO_INCREMENT,
    -> type_name VARCHAR(8)
    -> );
Query OK, 0 rows affected (0.04 sec)

• 用分组查询查看剑分类：

mysql> SELECT type FROM sword GROUP BY type;
+--------+
| type   |
+--------+
| 人界   |
| 仙界   |
| 神界   |
| 道界   |
| 鬼界   |
| 魔界   |
+--------+
6 rows in set (0.00 sec)

☆☆☆☆☆将查询的结果写入另一个数据表：

• 根据type的分组，通过sword的type字段，插入到sword_type表中的type_name字段

mysql> INSERT sword_type (type_name) SELECT type FROM sword GROUP BY type;
Query OK, 6 rows affected (0.00 sec)
Records: 6  Duplicates: 0  Warnings: 0

mysql> SELECT*FROM  sword_type;
+---------+-----------+
| type_id | type_name |
+---------+-----------+
|       1 | 人界      |
|       2 | 仙界      |
|       3 | 神界      |
|       4 | 道界      |
|       5 | 鬼界      |
|       6 | 魔界      |
+---------+-----------+
6 rows in set (0.00 sec)

☆☆☆☆☆

使用type_id更新sword中的数据

mysql>  UPDATE sword INNER JOIN sword_type
    ->   ON type = type_name
    ->   SET type = type_id ;
Query OK, 8 rows affected (0.00 sec)
Rows matched: 8  Changed: 8  Warnings: 0

mysql> SELECT*FROM sword;
+----+--------+-------+------+-------+------+------+
| id | name   | atk   | hit  | crit  | attr | type |
+----+--------+-------+------+-------+------+------+
|  1 | 黑风   | 10800 |  400 |   400 | 木   | 3    |
|  2 | 木藜   |  5400 |  200 |   200 | 木   | 1    |
|  3 | 荆戈   |  8020 | 1000 |    10 | 金   | 6    |
|  4 | 痕兮   |  8998 |  800 |   999 | 水   | 4    |
|  5 | 逐暮   |   100 | 1000 | 10000 | 火   | 5    |
|  6 | 风跃   |  9020 |   10 |    10 | 木   | 2    |
|  8 | 洛神   | 20020 |    1 |    10 | 金   | 3    |
|  9 | 隐锋   |  8020 | 2000 |    10 | 土   | 1    |
+----+--------+-------+------+-------+------+------+
8 rows in set (0.00 sec)

通过CREATE...SELECT来创建数据表并且同时写入记录

此时字段值必须为sword中的attr

mysql> CREATE TABLE sword_attr (
    -> attr_id SMALLINT UNSIGNED PRIMARY KEY AUTO_INCREMENT,
    -> attr VARCHAR(4) NOT NULL
    -> ) SELECT attr FROM sword GROUP BY attr;
Query OK, 5 rows affected (0.47 sec)
Records: 5  Duplicates: 0  Warnings: 0
mysql> SELECT*FROM sword_attr;
+---------+------+
| attr_id | attr |
+---------+------+
|       1 | 土   |
|       2 | 木   |
|       3 | 水   |
|       4 | 火   |
|       5 | 金   |
+---------+------+
5 rows in set (0.00 sec)

如果两表字段相同，这样会报错，需具体指定字段属于哪张表

• 错误：

mysql>   UPDATE sword INNER JOIN sword_attr
    ->   ON attr = attr
    ->   SET attr = attr_id;
ERROR 1052 (23000): Column 'attr' in field list is ambiguous

• 正确

mysql>   UPDATE sword AS s INNER JOIN sword_attr AS a
    ->   ON s.attr = a.attr
    ->   SET s.attr = a.attr_id;
Query OK, 8 rows affected (0.00 sec)
Rows matched: 8  Changed: 8  Warnings: 0

mysql> SELECT*FROM sword;
+----+--------+-------+------+-------+------+------+
| id | name   | atk   | hit  | crit  | attr | type |
+----+--------+-------+------+-------+------+------+
|  1 | 黑风   | 10800 |  400 |   400 | 2    | 3    |
|  2 | 木藜   |  5400 |  200 |   200 | 2    | 1    |
|  3 | 荆戈   |  8020 | 1000 |    10 | 5    | 6    |
|  4 | 痕兮   |  8998 |  800 |   999 | 3    | 4    |
|  5 | 逐暮   |   100 | 1000 | 10000 | 4    | 5    |
|  6 | 风跃   |  9020 |   10 |    10 | 2    | 2    |
|  8 | 洛神   | 20020 |    1 |    10 | 5    | 3    |
|  9 | 隐锋   |  8020 | 2000 |    10 | 1    | 1    |
+----+--------+-------+------+-------+------+------+
8 rows in set (0.00 sec)

查看一下表信息：

mysql> DESC sword;
+-------+----------------------+------+-----+---------+----------------+
| Field | Type                 | Null | Key | Default | Extra          |
+-------+----------------------+------+-----+---------+----------------+
| id    | smallint(5) unsigned | NO   | PRI | NULL    | auto_increment |
| name  | varchar(32)          | NO   |     | NULL    |                |
| atk   | smallint(5) unsigned | NO   |     | NULL    |                |
| hit   | smallint(5) unsigned | NO   |     | NULL    |                |
| crit  | smallint(5) unsigned | YES  |     | 10      |                |
| attr  | varchar(4)           | NO   |     | NULL    |                |
| type  | varchar(8)           | NO   |     | NULL    |                |
+-------+----------------------+------+-----+---------+----------------+
7 rows in set (0.00 sec)

此时可以改attr和type的类型为数字，

mysql>  ALTER TABLE sword
    ->   CHANGE type type_id SMALLINT UNSIGNED NOT NULL,
    ->   CHANGE attr attr_id SMALLINT UNSIGNED NOT NULL;
Query OK, 9 rows affected (0.05 sec)
Records: 9  Duplicates: 0  Warnings: 0

mysql> SELECT*FROM sword;
+----+--------+-------+------+-------+---------+---------+
| id | name   | atk   | hit  | crit  | attr_id | type_id |
+----+--------+-------+------+-------+---------+---------+
|  1 | 黑风   | 10800 |  400 |   400 |       2 |       3 |
|  2 | 木藜   |  5400 |  200 |   200 |       2 |       1 |
|  3 | 荆戈   |  8020 | 1000 |    10 |       5 |       6 |
|  4 | 痕兮   |  8998 |  800 |   999 |       3 |       4 |
|  5 | 逐暮   |   100 | 1000 | 10000 |       4 |       5 |
|  6 | 风跃   |  9020 |   10 |    10 |       2 |       2 |
|  8 | 洛神   | 20020 |    1 |    10 |       5 |       3 |
|  9 | 隐锋   |  8020 | 2000 |    10 |       1 |       1 |
+----+--------+-------+------+-------+---------+---------+
9 rows in set (0.01 sec)

mysql> DESC sword;
+---------+----------------------+------+-----+---------+----------------+
| Field   | Type                 | Null | Key | Default | Extra          |
+---------+----------------------+------+-----+---------+----------------+
| id      | smallint(5) unsigned | NO   | PRI | NULL    | auto_increment |
| name    | varchar(32)          | NO   |     | NULL    |                |
| atk     | smallint(5) unsigned | NO   |     | NULL    |                |
| hit     | smallint(5) unsigned | NO   |     | NULL    |                |
| crit    | smallint(5) unsigned | YES  |     | 10      |                |
| attr_id | smallint(5) unsigned | NO   |     | NULL    |                |
| type_id | smallint(5) unsigned | NO   |     | NULL    |                |
+---------+----------------------+------+-----+---------+----------------+
7 rows in set (0.00 sec)

这样表中两列重复汉字都用数字等价替换，减少表的体积。

表连接

添加两条类型

mysql> INSERT sword_type(type_name) VALUES('兽界'),('佛界');
Query OK, 2 rows affected (0.42 sec)
Records: 2  Duplicates: 0  Warnings: 0
mysql> SELECT*FROM sword_type;
+---------+-----------+
| type_id | type_name |
+---------+-----------+
|       1 | 人界      |
|       2 | 仙界      |
|       3 | 神界      |
|       4 | 道界      |
|       5 | 鬼界      |
|       6 | 魔界      |
|       7 | 兽界      |
|       8 | 佛界      |
+---------+-----------+
8 rows in set (0.00 sec)

添加两条属性

mysql> INSERT sword_attr(attr) VALUES('光'),('暗');
Query OK, 2 rows affected (0.00 sec)
Records: 2  Duplicates: 0  Warnings: 0

mysql> SELECT*FROM sword_attr;
+---------+------+
| attr_id | attr |
+---------+------+
|       1 | 土   |
|       2 | 木   |
|       3 | 水   |
|       4 | 火   |
|       5 | 金   |
|       6 | 光   |
|       7 | 暗   |
+---------+------+
7 rows in set (0.01 sec)

插入一条数据:弑神(attr_id越界)

mysql> INSERT sword VALUES(NULL,'弑神',12000,100,100,10,6);
Query OK, 1 row affected (0.00 sec)

mysql> SELECT*FROM sword;
+----+--------+-------+------+-------+---------+---------+
| id | name   | atk   | hit  | crit  | attr_id | type_id |
+----+--------+-------+------+-------+---------+---------+
|  1 | 黑风   | 10800 |  400 |   400 |       2 |       3 |
|  2 | 木藜   |  5400 |  200 |   200 |       2 |       1 |
|  3 | 荆戈   |  8020 | 1000 |    10 |       5 |       6 |
|  4 | 痕兮   |  8998 |  800 |   999 |       3 |       4 |
|  5 | 逐暮   |   100 | 1000 | 10000 |       4 |       5 |
|  6 | 风跃   |  9020 |   10 |    10 |       2 |       2 |
|  8 | 洛神   | 20020 |    1 |    10 |       5 |       3 |
|  9 | 隐锋   |  8020 | 2000 |    10 |       1 |       1 |
| 10 | 弑神   | 12000 |  100 |   100 |       10|       6 |
+----+--------+-------+------+-------+---------+---------+
10 rows in set (0.00 sec)

INNER JOIN

查询所有剑的详细信息(通过内连接实现:只呈现正确连接的记录)
由于弑神的attr_id越界，连接不正确，故无法查出

mysql> SELECT id,name,atk,hit,type_name,attr FROM sword AS s
    ->    INNER JOIN sword_type AS t ON s.type_id = t.type_id
    ->    INNER JOIN sword_attr AS a ON s.attr_id = a.attr_id;
+----+--------+-------+------+-----------+------+
| id | name   | atk   | hit  | type_name | attr |
+----+--------+-------+------+-----------+------+
|  1 | 黑风   | 10800 |  400 | 神界      | 木   |
|  2 | 木藜   |  5400 |  200 | 人界      | 木   |
|  3 | 荆戈   |  8020 | 1000 | 魔界      | 金   |
|  4 | 痕兮   |  8998 |  800 | 道界      | 水   |
|  5 | 逐暮   |   100 | 1000 | 鬼界      | 火   |
|  6 | 风跃   |  9020 |   10 | 仙界      | 木   |
|  8 | 洛神   | 20020 |    1 | 神界      | 金   |
|  9 | 隐锋   |  8020 | 2000 | 人界      | 土   |
+----+--------+-------+------+-----------+------+
8 rows in set (0.00 sec)

LEFT JOIN

查询所有剑的详细信息(左外连接：左表全部，右表无匹配则置空)

mysql> SELECT id,name,atk,hit,type_name,attr FROM sword AS s
    ->    LEFT JOIN sword_type AS t ON s.type_id = t.type_id
    ->    LEFT JOIN sword_attr AS a ON s.attr_id = a.attr_id;
+----+--------+-------+------+-----------+------+
| id | name   | atk   | hit  | type_name | attr |
+----+--------+-------+------+-----------+------+
|  1 | 黑风   | 10800 |  400 | 神界      | 木   |
|  2 | 木藜   |  5400 |  200 | 人界      | 木   |
|  3 | 荆戈   |  8020 | 1000 | 魔界      | 金   |
|  4 | 痕兮   |  8998 |  800 | 道界      | 水   |
|  5 | 逐暮   |   100 | 1000 | 鬼界      | 火   |
|  6 | 风跃   |  9020 |   10 | 仙界      | 木   |
|  8 | 洛神   | 20020 |    1 | 神界      | 金   |
|  9 | 隐锋   |  8020 | 2000 | 人界      | 土   |
| 10 | 弑神   | 12000 |  100 | 魔界      | NULL |
+----+--------+-------+------+-----------+------+
9 rows in set (0.00 sec)

RIGHT JOIN

查询所有剑的详细信息(左外连接：右表全部，左表无匹配则置空)

mysql> SELECT id,name,atk,hit,type_name,attr FROM sword AS s
    ->    RIGHT JOIN sword_type AS t ON s.type_id = t.type_id
    ->    RIGHT JOIN sword_attr AS a ON s.attr_id = a.attr_id;
+------+--------+-------+------+-----------+------+
| id   | name   | atk   | hit  | type_name | attr |
+------+--------+-------+------+-----------+------+
|    9 | 隐锋   |  8020 | 2000 | 人界      | 土   |
|    1 | 黑风   | 10800 |  400 | 神界      | 木   |
|    2 | 木藜   |  5400 |  200 | 人界      | 木   |
|    6 | 风跃   |  9020 |   10 | 仙界      | 木   |
|    4 | 痕兮   |  8998 |  800 | 道界      | 水   |
|    5 | 逐暮   |   100 | 1000 | 鬼界      | 火   |
|    3 | 荆戈   |  8020 | 1000 | 魔界      | 金   |
|    8 | 洛神   | 20020 |    1 | 神界      | 金   |
| NULL | NULL   |  NULL | NULL | NULL      | 光   |
| NULL | NULL   |  NULL | NULL | NULL      | 暗   |
+------+--------+-------+------+-----------+------+
10 rows in set (0.00 sec)