09.MySQL子查询和连接

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：所有攻击力格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)