SQL语言（二）
INSERT
-
语法一
语法：INSERT [LOW_PRIORITY | DELAYED | HIGH_PRIORITY] [IGNORE] [INTO] tbl_name [(col_name,...)] {VALUES | VALUE} ({expr | DEFAULT},...),(...),... [ ON DUPLICATE KEY UPDATE col_name=expr [, col_name=expr] ... ]
INSERT System_List VALUES(1,'RedHat','CentOS',7.5);
INSERT System_List(system_id,system_name,system_release) VALUES(2,'Debian','Ubuntu');MariaDB [testdb1]> SELECT * FROM System_List;
+-----------+-------------+----------------+----------------+
| system_id | system_name | system_release | system_version |
+-----------+-------------+----------------+----------------+
| 1 | RedHat | CentOS | 7.5 |
| 2 | Debian | Ubuntu | NULL |
+-----------+-------------+----------------+----------------+
2 rows in set (0.00 sec)
-
语法二
语法：INSERT [LOW_PRIORITY | DELAYED | HIGH_PRIORITY] [IGNORE] [INTO] tbl_name SET col_name={expr | DEFAULT}, ... [ ON DUPLICATE KEY UPDATE col_name=expr [, col_name=expr] ... ]
INSERT System_List SET system_id=3, system_name='RedHat', system_release='REHL', system_version=7.4;MariaDB [testdb1]> SELECT * FROM System_List;
+-----------+-------------+----------------+----------------+
| system_id | system_name | system_release | system_version |
+-----------+-------------+----------------+----------------+
| 1 | RedHat | CentOS | 7.5 |
| 2 | Debian | Ubuntu | NULL |
| 3 | RedHat | REHL | 7.4 |
+-----------+-------------+----------------+----------------+
3 rows in set (0.00 sec)
-
语法三
语法：INSERT [LOW_PRIORITY | HIGH_PRIORITY] [IGNORE] [INTO] tbl_name [(col_name,...)] SELECT ... [ ON DUPLICATE KEY UPDATE col_name=expr [, col_name=expr] ... ]
INSERT testable2(user,host) SELECT system_name,system_release FROM System_List;MariaDB [testdb1]> SELECT * FROM testable2;
+--------+------------------+-------------------------------------------+
| user | host | password |
+--------+------------------+-------------------------------------------+
| RedHat | CentOS | |
| Debian | Ubuntu | |
| RedHat | REHL | |
+--------+------------------+-------------------------------------------+
3 rows in set (0.00 sec)
UPDATE
语法：UPDATE [LOW_PRIORITY] [IGNORE] table_reference SET col_name1={expr1|DEFAULT} [, col_name2={expr2|DEFAULT}] ... [WHERE where_condition] [ORDER BY ...] [LIMIT row_count]
UPDATE System_List SET system_release='Fedora',system_version=28 WHERE system_id=1;MariaDB [testdb1]> SELECT * FROM System_List;
+-----------+-------------+----------------+----------------+
| system_id | system_name | system_release | system_version |
+-----------+-------------+----------------+----------------+
| 1 | RedHat | Fedora | 28 |
| 2 | Debian | Ubuntu | NULL |
| 3 | RedHat | REHL | 7.4 |
+-----------+-------------+----------------+----------------+
3 rows in set (0.00 sec)DELETE
语法：DELETE [LOW_PRIORITY] [QUICK] [IGNORE] FROM tbl_name [WHERE where_condition] [ORDER BY ...] [LIMIT row_count]
DELETE FROM System_List WHERE system_id=2;删除操作极为危险，所以在生产环境中尽量避免使用。可以在表中添加一个字段，作为标记位。当标记位为指定的值时，我们便将该字段判定为已删除。同时，当登录 MySQL 客户端时，指定 --safe-updates 或者 -U 选项，以保证当对表进行修改时，必须使用 WHERE 关键字
MariaDB [testdb1]> DALETE FROM System_List;
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'DALETE FROM System_List' at line 1
当然，在生产中也难以避免对表的删除需求。此时使用 DELETE 对表进行删除的效率就会非常笨重，但优点是当误删除时，可以通过日志进行回滚。也可以使用 TRUNCATE TABLE tbl_name 对整张表进行删除，此操作高效，但是不可回滚，非常危险！！！
SELECT
-
单表查询
简单查询
--'*'表示所有字段
SELECT * FROM System_List;
+-----------+-------------+----------------+----------------+
| system_id | system_name | system_release | system_version |
+-----------+-------------+----------------+----------------+
| 1 | RedHat | Fedora | 28 |
| 2 | Debian | Ubuntu | 18.4 |
| 3 | RedHat | REHL | 7.4 |
| 4 | Debian | Mint | 19 |
| 5 | RedHat | CentOS | 7.5 |
+-----------+-------------+----------------+----------------+
5 rows in set (0.00 sec)
SELECT system_release FROM System_List;
+----------------+
| system_release |
+----------------+
| Fedora |
| Ubuntu |
| REHL |
| Mint |
| CentOS |
+----------------+
5 rows in set (0.00 sec)
WHERE子句
| 操作符 | 功能 |
|---|---|
| = | 等于 |
| <> | 不等于 |
| > | 大于 |
| < | 小于 |
| >= | 大于等于 |
| <= | 小于等于 |
| BETWEEN X AND Y | 在X与Y之间 |
| LIKE | 模糊匹配 |
| IN | 包含 |
| IS [NOT] NULL | 是否为空 |
注：RLIKE 用于通过正则表达式匹配，但是不推荐使用。因为 RLIKE 子句将会使索引失效。
SELECT * FROM System_List WHERE system_id >= 2 ;
+-----------+-------------+----------------+----------------+
| system_id | system_name | system_release | system_version |
+-----------+-------------+----------------+----------------+
| 2 | Debian | Ubuntu | 18.4 |
| 3 | RedHat | REHL | 7.4 |
| 4 | Debian | Mint | 19 |
| 5 | RedHat | CentOS | 7.5 |
+-----------+-------------+----------------+----------------+
4 rows in set (0.00 sec)
SELECT * FROM System_List WHERE system_id BETWEEN 2 AND 5;
+-----------+-------------+----------------+----------------+
| system_id | system_name | system_release | system_version |
+-----------+-------------+----------------+----------------+
| 2 | Debian | Ubuntu | 18.4 |
| 3 | RedHat | REHL | 7.4 |
| 4 | Debian | Mint | 19 |
| 5 | RedHat | CentOS | 7.5 |
+-----------+-------------+----------------+----------------+
4 rows in set (0.00 sec)
--'%'用于表示任意个数任意字符
SELECT * FROM System_List WHERE system_name LIKE 'D%';
+-----------+-------------+----------------+----------------+
| system_id | system_name | system_release | system_version |
+-----------+-------------+----------------+----------------+
| 2 | Debian | Ubuntu | 18.4 |
| 4 | Debian | Mint | 19 |
+-----------+-------------+----------------+----------------+
2 rows in set (0.00 sec)
--'_'用于表示单个任意字符
SELECT * FROM System_List WHERE system_release LIKE '____';
+-----------+-------------+----------------+----------------+
| system_id | system_name | system_release | system_version |
+-----------+-------------+----------------+----------------+
| 3 | RedHat | REHL | 7.4 |
| 4 | Debian | Mint | 19 |
+-----------+-------------+----------------+----------------+
2 rows in set (0.00 sec)SELECT * FROM System_List WHERE system_name IN ('RedHat');
+-----------+-------------+----------------+----------------+
| system_id | system_name | system_release | system_version |
+-----------+-------------+----------------+----------------+
| 1 | RedHat | Fedora | 28 |
| 3 | RedHat | REHL | 7.4 |
| 5 | RedHat | CentOS | 7.5 |
+-----------+-------------+----------------+----------------+
3 rows in set (0.00 sec)
SELECT * FROM System_List WHERE system_name IS NULL ;
+-----------+-------------+----------------+----------------+
| system_id | system_name | system_release | system_version |
+-----------+-------------+----------------+----------------+
| 6 | NULL | SESU | 42.3 |
+-----------+-------------+----------------+----------------+
1 row in set (0.00 sec)
DISTINCT子句
--DISTINCT子句用于过滤重复行
SELECT DISTINCT system_name FROM System_List;
+-------------+
| system_name |
+-------------+
| RedHat |
| Debian |
| NULL |
+-------------+
3 rows in set (0.00 sec)
逻辑操作
--AND表示逻辑与 NOT表示逻辑非
SELECT * FROM System_List WHERE NOT system_id = 3 AND system_name = 'RedHat';
+-----------+-------------+----------------+----------------+
| system_id | system_name | system_release | system_version |
+-----------+-------------+----------------+----------------+
| 1 | RedHat | Fedora | 28 |
| 5 | RedHat | CentOS | 7.5 |
+-----------+-------------+----------------+----------------+
2 rows in set (0.00 sec)
--OR表示逻辑或
SELECT * FROM System_List WHERE system_id = 4 OR system_name = 'RedHat';
+-----------+-------------+----------------+----------------+
| system_id | system_name | system_release | system_version |
+-----------+-------------+----------------+----------------+
| 1 | RedHat | Fedora | 28 |
| 3 | RedHat | REHL | 7.4 |
| 4 | Debian | Mint | 19 |
| 5 | RedHat | CentOS | 7.5 |
+-----------+-------------+----------------+----------------+
4 rows in set (0.00 sec)AS子句
SELECT system_id AS ID, system_name AS NAME FROM System_List AS LIST;
+----+--------+
| ID | NAME |
+----+--------+
| 1 | RedHat |
| 2 | Debian |
| 3 | RedHat |
| 4 | Debian |
| 5 | RedHat |
| 6 | NULL |
+----+--------+
6 rows in set (0.00 sec)
GROUP
--当分组查询指令逻辑不通时，将会打印每组的第一个字段
SELECT system_used FROM System_List GROUP BY system_name;
+-------------+
| system_used |
+-------------+
| 40 |
| 100 |
| 30 |
+-------------+
3 rows in set (0.00 sec)
--max()函数用于统计字段中的最大值,min()相反
SELECT system_name, MAX(system_used) AS Max_System FROM System_List GROUP BY system_name;
+-------------+------------+
| system_name | Max_System |
+-------------+------------+
| NULL | 40 |
| Debian | 100 |
| RedHat | 120 |
+-------------+------------+
3 rows in set (0.00 sec)
--avg()函数用于计算平均数
SELECT system_name, AVG(system_used) AS Avg_System FROM System_List GROUP BY system_name;
+-------------+------------+
| system_name | Avg_System |
+-------------+------------+
| NULL | 40.0000 |
| Debian | 55.0000 |
| RedHat | 66.6667 |
+-------------+------------+
3 rows in set (0.00 sec)
--当分组以后，需要进行条件判断时必须使用HAVING子句
SELECT system_name, system_support, avg(system_used)
-> FROM System_List GROUP BY system_name, system_support
-> HAVING avg(system_used) > 50;
+-------------+----------------+------------------+
| system_name | system_support | avg(system_used) |
+-------------+----------------+------------------+
| Debian | P | 55.0000 |
| RedHat | V | 85.0000 |
+-------------+----------------+------------------+
2 rows in set (0.00 sec)ORDER
--ORDER子句默认使用ASC选项，升序排列
SELECT * FROM System_List ORDER BY system_used;
+-----------+-------------+----------------+----------------+-------------+----------------+
| system_id | system_name | system_release | system_version | system_used | system_support |
+-----------+-------------+----------------+----------------+-------------+----------------+
| 4 | Debian | Mint | 19 | 10 | P |
| 1 | RedHat | Fedora | 28 | 30 | P |
| 6 | NULL | SESU | 42.3 | 40 | V |
| 3 | RedHat | REHL | 7.4 | 50 | V |
| 2 | Debian | Ubuntu | 18.4 | 100 | P |
| 5 | RedHat | CentOS | 7.5 | 120 | V |
+-----------+-------------+----------------+----------------+-------------+----------------+
6 rows in set (0.00 sec)
--使用DESC选项以倒序排列打印
SELECT * FROM System_List ORDER BY system_used DESC;
+-----------+-------------+----------------+----------------+-------------+----------------+
| system_id | system_name | system_release | system_version | system_used | system_support |
+-----------+-------------+----------------+----------------+-------------+----------------+
| 5 | RedHat | CentOS | 7.5 | 120 | V |
| 2 | Debian | Ubuntu | 18.4 | 100 | P |
| 3 | RedHat | REHL | 7.4 | 50 | V |
| 6 | NULL | SESU | 42.3 | 40 | V |
| 1 | RedHat | Fedora | 28 | 30 | P |
| 4 | Debian | Mint | 19 | 10 | P |
+-----------+-------------+----------------+----------------+-------------+----------------+
6 rows in set (0.00 sec)
--对字符串进行排序时将会根据字符的先后顺序排列打印
SELECT * FROM System_List ORDER BY system_release;
+-----------+-------------+----------------+----------------+-------------+----------------+
| system_id | system_name | system_release | system_version | system_used | system_support |
+-----------+-------------+----------------+----------------+-------------+----------------+
| 5 | RedHat | CentOS | 7.5 | 120 | V |
| 1 | RedHat | Fedora | 28 | 30 | P |
| 4 | Debian | Mint | 19 | 10 | P |
| 3 | RedHat | REHL | 7.4 | 50 | V |
| 6 | NULL | SESU | 42.3 | 40 | V |
| 2 | Debian | Ubuntu | 18.4 | 100 | P |
+-----------+-------------+----------------+----------------+-------------+----------------+
6 rows in set (0.00 sec)
LIMIT
--LIMIT用于对输出的结果进行切割，可以同时定义'偏移量,字段数'
SELECT * FROM System_List ORDER BY system_release LIMIT 2,3;
+-----------+-------------+----------------+----------------+-------------+----------------+
| system_id | system_name | system_release | system_version | system_used | system_support |
+-----------+-------------+----------------+----------------+-------------+----------------+
| 4 | Debian | Mint | 19 | 10 | P |
| 3 | RedHat | REHL | 7.4 | 50 | V |
| 6 | NULL | SESU | 42.3 | 40 | V |
+-----------+-------------+----------------+----------------+-------------+----------------+
3 rows in set (0.00 sec)
-
多表查询
实验环境
show tables;
+-------------------+
| Tables_in_testdb2 |
+-------------------+
| course |
| score |
| student |
| teacher |
+-------------------+
4 rows in set (0.01 sec)
select * from course;
+-------+-----------------+-----+
| cno | cname | tno |
+-------+-----------------+-----+
| 3-105 | 计算机导论 | 825 |
| 3-245 | 操作系统 | 804 |
| 6-166 | 数字电路 | 856 |
| 9-888 | 高等数学 | 831 |
+-------+-----------------+-----+
4 rows in set (0.00 sec)
select * from score;
+-----+-------+--------+
| sno | cno | degree |
+-----+-------+--------+
| 101 | 3-105 | 64 |
| 103 | 3-105 | 92 |
| 103 | 3-245 | 86 |
| 103 | 6-166 | 85 |
| 105 | 3-105 | 88 |
| 105 | 3-245 | 75 |
| 105 | 6-166 | 79 |
| 107 | 3-105 | 91 |
| 108 | 3-105 | 78 |
| 109 | 3-105 | 76 |
| 109 | 3-245 | 68 |
| 109 | 6-166 | 81 |
+-----+-------+--------+
12 rows in set (0.01 sec)
select * from student;
+-----+--------+------+---------------------+-------+
| sno | sname | ssex | sbirthday | class |
+-----+--------+------+---------------------+-------+
| 101 | 李军 | 男 | 1976-02-20 00:00:00 | 95033 |
| 103 | 陆君 | 男 | 1974-06-03 00:00:00 | 95031 |
| 105 | 匡明 | 男 | 1975-10-02 00:00:00 | 95031 |
| 107 | 王丽 | 女 | 1976-01-23 00:00:00 | 95033 |
| 108 | 曾华 | 男 | 1977-09-01 00:00:00 | 95033 |
| 109 | 王芳 | 女 | 1975-02-10 00:00:00 | 95031 |
+-----+--------+------+---------------------+-------+
6 rows in set (0.02 sec)
select * from teacher;
+-----+--------+------+---------------------+-----------+-----------------+
| tno | tname | tsex | tbirthday | prof | depart |
+-----+--------+------+---------------------+-----------+-----------------+
| 804 | 李诚 | 男 | 1958-12-02 00:00:00 | 副教授 | 计算机系 |
| 825 | 王萍 | 女 | 1972-05-05 00:00:00 | 助教 | 计算机系 |
| 831 | 刘冰 | 女 | 1977-08-14 00:00:00 | 助教 | 电子工程系 |
| 856 | 张旭 | 男 | 1969-03-12 00:00:00 | 讲师 | 电子工程系 |
+-----+--------+------+---------------------+-----------+-----------------+
4 rows in set (0.00 sec)
内连接
SELECT st.sname, c.cname, sc.degree FROM student AS st INNER JOIN course AS c INNER JOIN score AS sc ON st.sno = sc.sno AND sc.cno = c.cno;
+--------+-----------------+--------+
| sname | cname | degree |
+--------+-----------------+--------+
| 李军 | 计算机导论 | 64 |
| 陆君 | 计算机导论 | 92 |
| 匡明 | 计算机导论 | 88 |
| 王丽 | 计算机导论 | 91 |
| 曾华 | 计算机导论 | 78 |
| 王芳 | 计算机导论 | 76 |
| 陆君 | 操作系统 | 86 |
| 匡明 | 操作系统 | 75 |
| 王芳 | 操作系统 | 68 |
| 陆君 | 数字电路 | 85 |
| 匡明 | 数字电路 | 79 |
| 王芳 | 数字电路 | 81 |
+--------+-----------------+--------+
12 rows in set (0.00 sec)
交叉连接
SELECT * FROM course CROSS JOIN teacher;
+-------+-----------------+-----+-----+--------+------+---------------------+-----------+-----------------+
| cno | cname | tno | tno | tname | tsex | tbirthday | prof | depart |
+-------+-----------------+-----+-----+--------+------+---------------------+-----------+-----------------+
| 3-105 | 计算机导论 | 825 | 804 | 李诚 | 男 | 1958-12-02 00:00:00 | 副教授 | 计算机系 |
| 3-245 | 操作系统 | 804 | 804 | 李诚 | 男 | 1958-12-02 00:00:00 | 副教授 | 计算机系 |
| 6-166 | 数字电路 | 856 | 804 | 李诚 | 男 | 1958-12-02 00:00:00 | 副教授 | 计算机系 |
| 9-888 | 高等数学 | 831 | 804 | 李诚 | 男 | 1958-12-02 00:00:00 | 副教授 | 计算机系 |
| 3-105 | 计算机导论 | 825 | 825 | 王萍 | 女 | 1972-05-05 00:00:00 | 助教 | 计算机系 |
| 3-245 | 操作系统 | 804 | 825 | 王萍 | 女 | 1972-05-05 00:00:00 | 助教 | 计算机系 |
| 6-166 | 数字电路 | 856 | 825 | 王萍 | 女 | 1972-05-05 00:00:00 | 助教 | 计算机系 |
| 9-888 | 高等数学 | 831 | 825 | 王萍 | 女 | 1972-05-05 00:00:00 | 助教 | 计算机系 |
| 3-105 | 计算机导论 | 825 | 831 | 刘冰 | 女 | 1977-08-14 00:00:00 | 助教 | 电子工程系 |
| 3-245 | 操作系统 | 804 | 831 | 刘冰 | 女 | 1977-08-14 00:00:00 | 助教 | 电子工程系 |
| 6-166 | 数字电路 | 856 | 831 | 刘冰 | 女 | 1977-08-14 00:00:00 | 助教 | 电子工程系 |
| 9-888 | 高等数学 | 831 | 831 | 刘冰 | 女 | 1977-08-14 00:00:00 | 助教 | 电子工程系 |
| 3-105 | 计算机导论 | 825 | 856 | 张旭 | 男 | 1969-03-12 00:00:00 | 讲师 | 电子工程系 |
| 3-245 | 操作系统 | 804 | 856 | 张旭 | 男 | 1969-03-12 00:00:00 | 讲师 | 电子工程系 |
| 6-166 | 数字电路 | 856 | 856 | 张旭 | 男 | 1969-03-12 00:00:00 | 讲师 | 电子工程系 |
| 9-888 | 高等数学 | 831 | 856 | 张旭 | 男 | 1969-03-12 00:00:00 | 讲师 | 电子工程系 |
+-------+-----------------+-----+-----+--------+------+---------------------+-----------+-----------------+
16 rows in set (0.00 sec)
左外连接
SELECT c.cname, s.degree FROM course AS c LEFT OUTER JOIN score AS s ON s.cno = c.cno;
+-----------------+--------+
| cname | degree |
+-----------------+--------+
| 计算机导论 | 64 |
| 计算机导论 | 92 |
| 计算机导论 | 88 |
| 计算机导论 | 91 |
| 计算机导论 | 78 |
| 计算机导论 | 76 |
| 操作系统 | 86 |
| 操作系统 | 75 |
| 操作系统 | 68 |
| 数字电路 | 85 |
| 数字电路 | 79 |
| 数字电路 | 81 |
| 高等数学 | NULL |
+-----------------+--------+
13 rows in set (0.01 sec)
右外连接与左外连接一样，只是左右顺序的调整，这里不再赘述。
全外连接
SELECT sno, sname, ssex, sbirthday FROM student
-> union
-> SELECT tno, tname, tsex, tbirthday FROM teacher;
+-----+--------+------+---------------------+
| sno | sname | ssex | sbirthday |
+-----+--------+------+---------------------+
| 101 | 李军 | 男 | 1976-02-20 00:00:00 |
| 103 | 陆君 | 男 | 1974-06-03 00:00:00 |
| 105 | 匡明 | 男 | 1975-10-02 00:00:00 |
| 107 | 王丽 | 女 | 1976-01-23 00:00:00 |
| 108 | 曾华 | 男 | 1977-09-01 00:00:00 |
| 109 | 王芳 | 女 | 1975-02-10 00:00:00 |
| 804 | 李诚 | 男 | 1958-12-02 00:00:00 |
| 825 | 王萍 | 女 | 1972-05-05 00:00:00 |
| 831 | 刘冰 | 女 | 1977-08-14 00:00:00 |
| 856 | 张旭 | 男 | 1969-03-12 00:00:00 |
+-----+--------+------+---------------------+
10 rows in set (0.01 sec)
全外连接就是使用 UNION 子句将两个外连接表拼接起来，从而得到两个表的全集
自连接
SELECT t.sname AS 学生姓名, s.sname AS 教师姓名 FROM test AS s LEFT OUTER JOIN test AS t ON t.tid = s.sid where t.tid IS NOT NULL;
+--------------+--------------+
| 学生姓名 | 教师姓名 |
+--------------+--------------+
| 陆君 | 李诚 |
| 匡明 | 王萍 |
| 曾华 | 刘冰 |
| 王芳 | 张旭 |
+--------------+--------------+
4 rows in set (0.00 sec)
子查询
SELECT st.sname, sc.degree FROM student AS st LEFT OUTER JOIN score AS sc ON st.sno = sc.sno AND cno = "3-105" WHERE degree > (SELECT AVG(degree) FROM score);
+--------+--------+
| sname | degree |
+--------+--------+
| 陆君 | 92 |
| 匡明 | 88 |
| 王丽 | 91 |
+--------+--------+
3 rows in set (0.00 sec)