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)

转载于:https://www.cnblogs.com/toly-top/p/9782017.html