Mysql之查询语句
前言：
Mysql中查询语句是日常使用最频繁和复杂的语句，Mysql查询有单表查询和多表连接查询，以下通过案例来熟悉Mysql的查询语句。
一、单表查询
现有hellodb数据库和students等表
mysql> SHOW DATABASES;
+--------------------+
| Database |
+--------------------+
| information_schema |
| dbtest |
| hellodb |
| mydb |
| mysql |
| performance_schema |
| sys |
| test |
| testdb |
+--------------------+
9 rows in set (0.00 sec)
mysql> USE hellodb;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A
mysql> SHOW TABLES;
+-------------------+
| Tables_in_hellodb |
+-------------------+
| classes |
| coc |
| courses |
| scores |
| students |
| teachers |
| test |
| toc |
+-------------------+
8 rows in set (0.00 sec)
查询Gender字段并去重
mysql> SELECT DISTINCT Gender FROM students;
+--------+
| Gender |
+--------+
| M |
| F |
+--------+
2 rows in set (0.00 sec)
查看缓存命中次数
mysql> SHOW GLOBAL STATUS LIKE 'Qcache%';
+-------------------------+----------+
| Variable_name | Value |
+-------------------------+----------+
| Qcache_free_blocks | 1 |
| Qcache_free_memory | 1031832 |
| Qcache_hits | 0 |
| Qcache_inserts | 0 |
| Qcache_lowmem_prunes | 0 |
| Qcache_not_cached | 34450935 |
| Qcache_queries_in_cache | 0 |
| Qcache_total_blocks | 1 |
+-------------------------+----------+
8 rows in set (0.00 sec)
查看查询的次数
mysql> SHOW GLOBAL STATUS LIKE 'Com_se%';
+----------------+----------+
| Variable_name | Value |
+----------------+----------+
| Com_select | 34450938 |
| Com_set_option | 53743714 |
+----------------+----------+
2 rows in set (0.01 sec)
命中率=(命中总次数/查询总次数)*100
查询字段使用别名
mysql> SELECT Name FROM students;
+---------------+
| Name |
+---------------+
| Diao Chan |
| Ding Dian |
| Duan Yu |
| Hua Rong |
| Huang Yueying |
| Jinjiao King |
| Lin Chong |
| Lin Daiyu |
| Lu Wushuang |
| Ma Chao |
| Ren Yingying |
| Shi Potian |
| Shi Qing |
| Shi Zhongyu |
| Sun Dasheng |
| Tian Boguang |
| Wen Qingqing |
| Xi Ren |
| Xiao Qiao |
| Xie Yanke |
| Xu Xian |
| Xu Zhu |
| Xue Baochai |
| Yinjiao King |
| Yu Yutong |
| Yuan Chengzhi |
| Yue Lingshan |
+---------------+
27 rows in set (0.00 sec)
mysql> SELECT Name AS StuName FROM students;
+---------------+
| StuName |
+---------------+
| Diao Chan |
| Ding Dian |
| Duan Yu |
| Hua Rong |
| Huang Yueying |
| Jinjiao King |
| Lin Chong |
| Lin Daiyu |
| Lu Wushuang |
| Ma Chao |
| Ren Yingying |
| Shi Potian |
| Shi Qing |
| Shi Zhongyu |
| Sun Dasheng |
| Tian Boguang |
| Wen Qingqing |
| Xi Ren |
| Xiao Qiao |
| Xie Yanke |
| Xu Xian |
| Xu Zhu |
| Xue Baochai |
| Yinjiao King |
| Yu Yutong |
| Yuan Chengzhi |
| Yue Lingshan |
+---------------+
27 rows in set (0.00 sec)
算数和比较操作符
mysql> SELECT Name,Age FROM students WHERE Age > 50;
+--------------+-----+
| Name | Age |
+--------------+-----+
| Xie Yanke | 53 |
| Yinjiao King | 98 |
| Sun Dasheng | 100 |
| Jinjiao King | 100 |
+--------------+-----+
4 rows in set (0.00 sec)
mysql> SELECT Name,Age FROM students WHERE Age+30 > 50;
+---------------+-----+
| Name | Age |
+---------------+-----+
| Shi Zhongyu | 22 |
| Shi Potian | 22 |
| Xie Yanke | 53 |
| Ding Dian | 32 |
| Yu Yutong | 26 |
| Shi Qing | 46 |
| Yuan Chengzhi | 23 |
| Tian Boguang | 33 |
| Xu Zhu | 21 |
| Lin Chong | 25 |
| Hua Rong | 23 |
| Huang Yueying | 22 |
| Ma Chao | 23 |
| Xu Xian | 27 |
| Sun Dasheng | 100 |
| Jinjiao King | 100 |
| Yinjiao King | 98 |
+---------------+-----+
17 rows in set (0.00 sec)
mysql> SELECT Name,Age FROM students WHERE Age != 50;
+---------------+-----+
| Name | Age |
+---------------+-----+
| Shi Zhongyu | 22 |
| Shi Potian | 22 |
| Xie Yanke | 53 |
| Ding Dian | 32 |
| Yu Yutong | 26 |
| Shi Qing | 46 |
| Xi Ren | 19 |
| Lin Daiyu | 17 |
| Ren Yingying | 20 |
| Yue Lingshan | 19 |
| Yuan Chengzhi | 23 |
| Wen Qingqing | 19 |
| Tian Boguang | 33 |
| Lu Wushuang | 17 |
| Duan Yu | 19 |
| Xu Zhu | 21 |
| Lin Chong | 25 |
| Hua Rong | 23 |
| Xue Baochai | 18 |
| Diao Chan | 19 |
| Huang Yueying | 22 |
| Xiao Qiao | 20 |
| Ma Chao | 23 |
| Xu Xian | 27 |
| Sun Dasheng | 100 |
| Jinjiao King | 100 |
| Yinjiao King | 98 |
+---------------+-----+
27 rows in set (0.00 sec)
mysql> SELECT Name,Age FROM students WHERE Age IN (18,100);
+--------------+-----+
| Name | Age |
+--------------+-----+
| Xue Baochai | 18 |
| Sun Dasheng | 100 |
| Jinjiao King | 100 |
+--------------+-----+
3 rows in set (0.00 sec)
mysql> SELECT Name,ClassID FROM students WHERE ClassID = NULL;
Empty set (0.00 sec)
mysql> SELECT Name,ClassID FROM students WHERE ClassID IS NULL;
+--------------+---------+
| Name | ClassID |
+--------------+---------+
| Xu Xian | NULL |
| Sun Dasheng | NULL |
| Jinjiao King | NULL |
| Yinjiao King | NULL |
+--------------+---------+
4 rows in set (0.00 sec)
根据性别进行分组
mysql> SELECT * FROM students GROUP BY Age;
+-------+---------------+-----+--------+---------+-----------+
| StuID | Name | Age | Gender | ClassID | TeacherID |
+-------+---------------+-----+--------+---------+-----------+
| 8 | Lin Daiyu | 17 | F | 7 | NULL |
| 19 | Xue Baochai | 18 | F | 6 | NULL |
| 7 | Xi Ren | 19 | F | 3 | NULL |
| 9 | Ren Yingying | 20 | F | 6 | NULL |
| 16 | Xu Zhu | 21 | M | 1 | NULL |
| 1 | Shi Zhongyu | 22 | M | 2 | 3 |
| 11 | Yuan Chengzhi | 23 | M | 6 | NULL |
| 17 | Lin Chong | 25 | M | 4 | NULL |
| 5 | Yu Yutong | 26 | M | 3 | 1 |
| 24 | Xu Xian | 27 | M | NULL | NULL |
| 4 | Ding Dian | 32 | M | 4 | 4 |
| 13 | Tian Boguang | 33 | M | 2 | NULL |
| 6 | Shi Qing | 46 | M | 5 | NULL |
| 3 | Xie Yanke | 53 | M | 2 | 16 |
| 27 | Yinjiao King | 98 | M | NULL | NULL |
| 25 | Sun Dasheng | 100 | M | NULL | NULL |
+-------+---------------+-----+--------+---------+-----------+
根据性别进行分组并且年龄做平均运算，根据性别显示
GROUP BY：根据指定的字段把查询的结果进行“分组”以用于“聚合”运算；
avg(), max(), min(), sum(), count()
HAVING：对分组聚合后的结果进行条件过滤；
mysql> SELECT avg(Age),Gender FROM students GROUP BY Gender;
+----------+--------+
| avg(Age) | Gender |
+----------+--------+
| 19.0000 | F |
| 40.7647 | M |
+----------+--------+
2 rows in set (0.00 sec)
统计每个班级的人数（对班级进行分组）
mysql> SELECT count(StuID) AS NOS,ClassID FROM students GROUP BY ClassID;
+-----+---------+
| NOS | ClassID |
+-----+---------+
| 4 | NULL |
| 4 | 1 |
| 3 | 2 |
| 4 | 3 |
| 4 | 4 |
| 1 | 5 |
| 4 | 6 |
| 3 | 7 |
+-----+---------+
8 rows in set (0.00 sec)
统计每个班级的人数并且大于2的
mysql> SELECT count(StuID) AS NOS,ClassID FROM students GROUP BY ClassID HAVING NOS>2;
+-----+---------+
| NOS | ClassID |
+-----+---------+
| 4 | NULL |
| 4 | 1 |
| 3 | 2 |
| 4 | 3 |
| 4 | 4 |
| 4 | 6 |
| 3 | 7 |
+-----+---------+
7 rows in set (0.01 sec)
根据年龄排序，降序
ORDER BY：根据指定的字段把查询的结果进行排序；默认升序；
升序：ASC
降序：DESC
mysql> SELECT Name,Age FROM students ORDER BY Age DESC;
+---------------+-----+
| Name | Age |
+---------------+-----+
| Jinjiao King | 100 |
| Sun Dasheng | 100 |
| Yinjiao King | 98 |
| Xie Yanke | 53 |
| Shi Qing | 46 |
| Tian Boguang | 33 |
| Ding Dian | 32 |
| Xu Xian | 27 |
| Yu Yutong | 26 |
| Lin Chong | 25 |
| Ma Chao | 23 |
| Yuan Chengzhi | 23 |
| Hua Rong | 23 |
| Huang Yueying | 22 |
| Shi Potian | 22 |
| Shi Zhongyu | 22 |
| Xu Zhu | 21 |
| Xiao Qiao | 20 |
| Ren Yingying | 20 |
| Duan Yu | 19 |
| Wen Qingqing | 19 |
| Diao Chan | 19 |
| Yue Lingshan | 19 |
| Xi Ren | 19 |
| Xue Baochai | 18 |
| Lu Wushuang | 17 |
| Lin Daiyu | 17 |
+---------------+-----+
27 rows in set (0.00 sec)
查询之后显示10行
LIMIT：对输出结果进行数量限制
[LIMIT {[offset,] row_count | row_count OFFSET offset}]
LIMIT 10:显示10行
LIMIT 10,10 :显示11-20行，偏移10行，显示后10行
mysql> SELECT Name,Age FROM students ORDER BY Age DESC LIMIT 10;
+--------------+-----+
| Name | Age |
+--------------+-----+
| Sun Dasheng | 100 |
| Jinjiao King | 100 |
| Yinjiao King | 98 |
| Xie Yanke | 53 |
| Shi Qing | 46 |
| Tian Boguang | 33 |
| Ding Dian | 32 |
| Xu Xian | 27 |
| Yu Yutong | 26 |
| Lin Chong | 25 |
+--------------+-----+
10 rows in set (0.00 sec)
mysql> SELECT Name,Age FROM students ORDER BY Age DESC LIMIT 10,10;
+---------------+-----+
| Name | Age |
+---------------+-----+
| Ma Chao | 23 |
| Yuan Chengzhi | 23 |
| Hua Rong | 23 |
| Huang Yueying | 22 |
| Shi Potian | 22 |
| Shi Zhongyu | 22 |
| Xu Zhu | 21 |
| Xiao Qiao | 20 |
| Ren Yingying | 20 |
| Duan Yu | 19 |
+---------------+-----+
10 rows in set (0.00 sec)
二、多表查询
交叉连接,笛卡尔乘积
连接查询的结果集中包含一个表中的每一条记录与另一个表中的每一条记录相互匹配的组合，像这样的结果集就可以称之为笛卡尔积。
不推荐此方法查询。
mysql> mysql> SELECT students;
+-------+---------------+-----+--------+---------+-----------+
| StuID | Name | Age | Gender | ClassID | TeacherID |
+-------+---------------+-----+--------+---------+-----------+
| 1 | Shi Zhongyu | 22 | M | 2 | 3 |
| 2 | Shi Potian | 22 | M | 1 | 7 |
| 3 | Xie Yanke | 53 | M | 2 | 16 |
| 4 | Ding Dian | 32 | M | 4 | 4 |
| 5 | Yu Yutong | 26 | M | 3 | 1 |
| 6 | Shi Qing | 46 | M | 5 | NULL |
| 7 | Xi Ren | 19 | F | 3 | NULL |
| 8 | Lin Daiyu | 17 | F | 7 | NULL |
| 9 | Ren Yingying | 20 | F | 6 | NULL |
| 10 | Yue Lingshan | 19 | F | 3 | NULL |
| 11 | Yuan Chengzhi | 23 | M | 6 | NULL |
| 12 | Wen Qingqing | 19 | F | 1 | NULL |
| 13 | Tian Boguang | 33 | M | 2 | NULL |
| 14 | Lu Wushuang | 17 | F | 3 | NULL |
| 15 | Duan Yu | 19 | M | 4 | NULL |
| 16 | Xu Zhu | 21 | M | 1 | NULL |
| 17 | Lin Chong | 25 | M | 4 | NULL |
| 18 | Hua Rong | 23 | M | 7 | NULL |
| 19 | Xue Baochai | 18 | F | 6 | NULL |
| 20 | Diao Chan | 19 | F | 7 | NULL |
| 21 | Huang Yueying | 22 | F | 6 | NULL |
| 22 | Xiao Qiao | 20 | F | 1 | NULL |
| 23 | Ma Chao | 23 | M | 4 | NULL |
| 24 | Xu Xian | 27 | M | NULL | NULL |
| 25 | Sun Dasheng | 100 | M | NULL | NULL |
| 26 | Jinjiao King | 100 | M | NULL | NULL |
| 27 | Yinjiao King | 98 | M | NULL | NULL |
+-------+---------------+-----+--------+---------+-----------+
27 rows in set (0.00 sec)
mysql> SELECT * FROM teachers;;
+-----+---------------+-----+--------+
| TID | Name | Age | Gender |
+-----+---------------+-----+--------+
| 1 | Song Jiang | 45 | M |
| 2 | Zhang Sanfeng | 94 | M |
| 3 | Miejue Shitai | 77 | F |
| 4 | Lin Chaoying | 93 | F |
+-----+---------------+-----+--------+
4 rows in set (0.00 sec)
mysql> SELECT * FROM students,teachers;;
+-------+---------------+-----+--------+---------+-----------+-----+---------------+-----+--------+
| StuID | Name | Age | Gender | ClassID | TeacherID | TID | Name | Age | Gender |
+-------+---------------+-----+--------+---------+-----------+-----+---------------+-----+--------+
| 1 | Shi Zhongyu | 22 | M | 2 | 3 | 1 | Song Jiang | 45 | M |
| 1 | Shi Zhongyu | 22 | M | 2 | 3 | 2 | Zhang Sanfeng | 94 | M |
| 1 | Shi Zhongyu | 22 | M | 2 | 3 | 3 | Miejue Shitai | 77 | F |
| 1 | Shi Zhongyu | 22 | M | 2 | 3 | 4 | Lin Chaoying | 93 | F |
| 2 | Shi Potian | 22 | M | 1 | 7 | 1 | Song Jiang | 45 | M |
| 2 | Shi Potian | 22 | M | 1 | 7 | 2 | Zhang Sanfeng | 94 | M |
| 2 | Shi Potian | 22 | M | 1 | 7 | 3 | Miejue Shitai | 77 | F |
| 2 | Shi Potian | 22 | M | 1 | 7 | 4 | Lin Chaoying | 93 | F |
| 3 | Xie Yanke | 53 | M | 2 | 16 | 1 | Song Jiang | 45 | M |
| 3 | Xie Yanke | 53 | M | 2 | 16 | 2 | Zhang Sanfeng | 94 | M |
| 3 | Xie Yanke | 53 | M | 2 | 16 | 3 | Miejue Shitai | 77 | F |
| 3 | Xie Yanke | 53 | M | 2 | 16 | 4 | Lin Chaoying | 93 | F |
| 4 | Ding Dian | 32 | M | 4 | 4 | 1 | Song Jiang | 45 | M |
| 4 | Ding Dian | 32 | M | 4 | 4 | 2 | Zhang Sanfeng | 94 | M |
| 4 | Ding Dian | 32 | M | 4 | 4 | 3 | Miejue Shitai | 77 | F |
| 4 | Ding Dian | 32 | M | 4 | 4 | 4 | Lin Chaoying | 93 | F |
| 5 | Yu Yutong | 26 | M | 3 | 1 | 1 | Song Jiang | 45 | M |
...
...
| 27 | Yinjiao King | 98 | M | NULL | NULL | 3 | Miejue Shitai | 77 | F |
| 27 | Yinjiao King | 98 | M | NULL | NULL | 4 | Lin Chaoying | 93 | F |
+-------+---------------+-----+--------+---------+-----------+-----+---------------+-----+--------+
108 rows in set (0.00 sec)
内连接
等值连接:
让表之间的字段以等值的方式建立连接，
两个表中具有相同意义的字段或具有关联的字段建立连接。
- 等值连接
mysql> SELECT * FROM students,teachers WHERE students.TeacherID=teachers.TID;
+-------+-------------+-----+--------+---------+-----------+-----+---------------+-----+--------+
| StuID | Name | Age | Gender | ClassID | TeacherID | TID | Name | Age | Gender |
+-------+-------------+-----+--------+---------+-----------+-----+---------------+-----+--------+
| 1 | Shi Zhongyu | 22 | M | 2 | 3 | 3 | Miejue Shitai | 77 | F |
| 4 | Ding Dian | 32 | M | 4 | 4 | 4 | Lin Chaoying | 93 | F |
| 5 | Yu Yutong | 26 | M | 3 | 1 | 1 | Song Jiang | 45 | M |
+-------+-------------+-----+--------+---------+-----------+-----+---------------+-----+--------+
3 rows in set (0.00 sec)
查询每个同学所属的门派
mysql> SELECT * FROM students;
+-------+---------------+-----+--------+---------+-----------+
| StuID | Name | Age | Gender | ClassID | TeacherID |
+-------+---------------+-----+--------+---------+-----------+
| 1 | Shi Zhongyu | 22 | M | 2 | 3 |
| 2 | Shi Potian | 22 | M | 1 | 7 |
| 3 | Xie Yanke | 53 | M | 2 | 16 |
| 4 | Ding Dian | 32 | M | 4 | 4 |
| 5 | Yu Yutong | 26 | M | 3 | 1 |
| 6 | Shi Qing | 46 | M | 5 | NULL |
| 7 | Xi Ren | 19 | F | 3 | NULL |
| 8 | Lin Daiyu | 17 | F | 7 | NULL |
| 9 | Ren Yingying | 20 | F | 6 | NULL |
| 10 | Yue Lingshan | 19 | F | 3 | NULL |
| 11 | Yuan Chengzhi | 23 | M | 6 | NULL |
| 12 | Wen Qingqing | 19 | F | 1 | NULL |
| 13 | Tian Boguang | 33 | M | 2 | NULL |
| 14 | Lu Wushuang | 17 | F | 3 | NULL |
| 15 | Duan Yu | 19 | M | 4 | NULL |
| 16 | Xu Zhu | 21 | M | 1 | NULL |
| 17 | Lin Chong | 25 | M | 4 | NULL |
| 18 | Hua Rong | 23 | M | 7 | NULL |
| 19 | Xue Baochai | 18 | F | 6 | NULL |
| 20 | Diao Chan | 19 | F | 7 | NULL |
| 21 | Huang Yueying | 22 | F | 6 | NULL |
| 22 | Xiao Qiao | 20 | F | 1 | NULL |
| 23 | Ma Chao | 23 | M | 4 | NULL |
| 24 | Xu Xian | 27 | M | NULL | NULL |
| 25 | Sun Dasheng | 100 | M | NULL | NULL |
| 26 | Jinjiao King | 100 | M | NULL | NULL |
| 27 | Yinjiao King | 98 | M | NULL | NULL |
+-------+---------------+-----+--------+---------+-----------+
27 rows in set (0.00 sec)
mysql> SELECT * FROM classes;
+---------+----------------+----------+
| ClassID | Class | NumOfStu |
+---------+----------------+----------+
| 1 | Shaolin Pai | 10 |
| 2 | Emei Pai | 7 |
| 3 | QingCheng Pai | 11 |
| 4 | Wudang Pai | 12 |
| 5 | Riyue Shenjiao | 31 |
| 6 | Lianshan Pai | 27 |
| 7 | Ming Jiao | 27 |
| 8 | Xiaoyao Pai | 15 |
+---------+----------------+----------+
8 rows in set (0.00 sec)
mysql> SELECT students.Name,classes.Class FROM students,classes WHERE students.ClassID=classes.ClassID;
+---------------+----------------+
| Name | Class |
+---------------+----------------+
| Shi Zhongyu | Emei Pai |
| Shi Potian | Shaolin Pai |
| Xie Yanke | Emei Pai |
| Ding Dian | Wudang Pai |
| Yu Yutong | QingCheng Pai |
| Shi Qing | Riyue Shenjiao |
| Xi Ren | QingCheng Pai |
| Lin Daiyu | Ming Jiao |
| Ren Yingying | Lianshan Pai |
| Yue Lingshan | QingCheng Pai |
| Yuan Chengzhi | Lianshan Pai |
| Wen Qingqing | Shaolin Pai |
| Tian Boguang | Emei Pai |
| Lu Wushuang | QingCheng Pai |
| Duan Yu | Wudang Pai |
| Xu Zhu | Shaolin Pai |
| Lin Chong | Wudang Pai |
| Hua Rong | Ming Jiao |
| Xue Baochai | Lianshan Pai |
| Diao Chan | Ming Jiao |
| Huang Yueying | Lianshan Pai |
| Xiao Qiao | Shaolin Pai |
| Ma Chao | Wudang Pai |
+---------------+----------------+
23 rows in set (0.00 sec)
- 自连接
mysql> SELECT s.Name,t.Name FROM students AS s,students AS t WHERE s.TeacherID=t.StuID;
+-------------+-------------+
| Name | Name |
+-------------+-------------+
| Shi Zhongyu | Xie Yanke |
| Shi Potian | Xi Ren |
| Xie Yanke | Xu Zhu |
| Ding Dian | Ding Dian |
| Yu Yutong | Shi Zhongyu |
+-------------+-------------+
5 rows in set (0.00 sec)
外连接
左外连接：以左边表为基准，建立连接，左右都有值的显示值，左边有的右边没有，显示为空。
右外连接：以右边表为基准，建立连接，左右都有值的显示值，右边有的左边没有，显示为空。
- 左外连接
mysql> mysql> SELECT s.Name,c.Class FROM students AS s LEFT JOIN classes AS c ON s.ClassID=c.ClassID;
+---------------+----------------+
| Name | Class |
+---------------+----------------+
| Shi Zhongyu | Emei Pai |
| Shi Potian | Shaolin Pai |
| Xie Yanke | Emei Pai |
| Ding Dian | Wudang Pai |
| Yu Yutong | QingCheng Pai |
| Shi Qing | Riyue Shenjiao |
| Xi Ren | QingCheng Pai |
| Lin Daiyu | Ming Jiao |
| Ren Yingying | Lianshan Pai |
| Yue Lingshan | QingCheng Pai |
| Yuan Chengzhi | Lianshan Pai |
| Wen Qingqing | Shaolin Pai |
| Tian Boguang | Emei Pai |
| Lu Wushuang | QingCheng Pai |
| Duan Yu | Wudang Pai |
| Xu Zhu | Shaolin Pai |
| Lin Chong | Wudang Pai |
| Hua Rong | Ming Jiao |
| Xue Baochai | Lianshan Pai |
| Diao Chan | Ming Jiao |
| Huang Yueying | Lianshan Pai |
| Xiao Qiao | Shaolin Pai |
| Ma Chao | Wudang Pai |
| Xu Xian | NULL |
| Sun Dasheng | NULL |
| Jinjiao King | NULL |
| Yinjiao King | NULL |
+---------------+----------------+
27 rows in set (0.00 sec)
- 右外连接
mysql> SELECT s.Name,c.Class FROM students AS s RIGHT JOIN classes AS c ON s.ClassID=c.ClassID;
+---------------+----------------+
| Name | Class |
+---------------+----------------+
| Shi Zhongyu | Emei Pai |
| Shi Potian | Shaolin Pai |
| Xie Yanke | Emei Pai |
| Ding Dian | Wudang Pai |
| Yu Yutong | QingCheng Pai |
| Shi Qing | Riyue Shenjiao |
| Xi Ren | QingCheng Pai |
| Lin Daiyu | Ming Jiao |
| Ren Yingying | Lianshan Pai |
| Yue Lingshan | QingCheng Pai |
| Yuan Chengzhi | Lianshan Pai |
| Wen Qingqing | Shaolin Pai |
| Tian Boguang | Emei Pai |
| Lu Wushuang | QingCheng Pai |
| Duan Yu | Wudang Pai |
| Xu Zhu | Shaolin Pai |
| Lin Chong | Wudang Pai |
| Hua Rong | Ming Jiao |
| Xue Baochai | Lianshan Pai |
| Diao Chan | Ming Jiao |
| Huang Yueying | Lianshan Pai |
| Xiao Qiao | Shaolin Pai |
| Ma Chao | Wudang Pai |
| NULL | Xiaoyao Pai |
+---------------+----------------+
24 rows in set (0.00 sec)
子查询
- 查询年龄大于平均年龄的同学
mysql> SELECT Name,Age FROM students WHERE Age> (SELECT avg(Age) FROM students);
+--------------+-----+
| Name | Age |
+--------------+-----+
| Tian Boguang | 33 |
| Shi Qing | 46 |
| Xie Yanke | 53 |
| Yinjiao King | 98 |
| Sun Dasheng | 100 |
| Jinjiao King | 100 |
+--------------+-----+
6 rows in set (0.00 sec)
- 用于IN中的子查询
mysql> SELECT Name,Age FROM students WHERE Age IN (SELECT Age FROM teachers);
Empty set (0.01 sec)
联合查询：将多个查询语句的执行结果相合并
mysql> SELECT Name,Age FROM students UNION SELECT Name,Age FROM teachers;
+---------------+-----+
| Name | Age |
+---------------+-----+
| Shi Zhongyu | 22 |
| Shi Potian | 22 |
| Xie Yanke | 53 |
| Ding Dian | 32 |
| Yu Yutong | 26 |
| Shi Qing | 46 |
| Xi Ren | 19 |
| Lin Daiyu | 17 |
| Ren Yingying | 20 |
| Yue Lingshan | 19 |
| Yuan Chengzhi | 23 |
| Wen Qingqing | 19 |
| Tian Boguang | 33 |
| Lu Wushuang | 17 |
| Duan Yu | 19 |
| Xu Zhu | 21 |
| Lin Chong | 25 |
| Hua Rong | 23 |
| Xue Baochai | 18 |
| Diao Chan | 19 |
| Huang Yueying | 22 |
| Xiao Qiao | 20 |
| Ma Chao | 23 |
| Xu Xian | 27 |
| Sun Dasheng | 100 |
| Jinjiao King | 100 |
| Yinjiao King | 98 |
| Song Jiang | 45 |
| Zhang Sanfeng | 94 |
| Miejue Shitai | 77 |
| Lin Chaoying | 93 |
+---------------+-----+
31 rows in set (0.00 sec)
Mysql之查询语句的更多相关文章
- 23个MySQL常用查询语句
23个MySQL常用查询语句 一查询数值型数据: SELECT * FROM tb_name WHERE sum > 100; 查询谓词:>,=,<,<>,!=,!> ...
- MySQL 表查询语句练习题
MySQL 表查询语句练习题: 一. 设有一数据库,包括四个表:学生表(Student).课程表(Course).成绩表(Score)以及教师信息表(Teacher).四个表的结构分别如表1-1的表 ...
- MYSQL——解题查询语句答题思路，再难的查询都不怕！
select查询语句,作为测试人员,使用此语句是家常便饭,是必须掌握的部分,由开始学习mysql到网上搜索试题做,开始做题一塌糊涂,拿到题目就晕,无从下手,现在慢慢总结了一套自己做题的方式,很开森,嘿 ...
- mysql—常用查询语句总结
关于MySQL常用的查询语句 一查询数值型数据: ; 查询谓词:>,=,<,<>,!=,!>,!<,=>,=< 二查询字符串 SELECT * FROM ...
- MySQL慢查询语句的定位
使用以下语句可以查询相关的配置和日志所在位置: show variables like '%slow%'; 名词解释: log_slow_admin_statements: 打开后可以将一些比较慢的管 ...
- Mysql的查询语句（联合查询、连接查询、子查询等）
Mysql的各个查询语句(联合查询.连接查询.子查询等) 一.联合查询 关键字:union 语法形式 select语句1 union[union选项] select 语句2 union[union选项 ...
- Mysql的查询语句的使用
1. 简单查询 查询所有字段: SELECT * FROM 表名 查询特定字段: SELECT 字段列表 FROM 表名 2. 查询显示行号 - 在字段列表中加入(@rownum := @rownum ...
- mysql命令查询语句&MTdata
1.单表查询 select * from student; 采用*效率低,不推荐,多用列名 一.单表查询的语法: SELECT 字段1,字段2... FROM 表名 WHERE 条件 GROUP BY ...
- mysql中查询语句中的一个知识点说明
1, 简单说明. select * from tb_name where 1[不为零即可];则会显示所有记录,select * from tb_name where 0;则不显示任何记录 假设数据库中 ...
- MySQL简单查询语句练习
数据查询语法(DQL) DQL就是数据查询语言,数据库执行DQL语句不会对数据进行改变,而是让数据库发送结果集给客户端. 语法: SELECT selection_list /*要查询的列名称*/ F ...
随机推荐
- Android\C++\C#\Java
关于:(38条消息) 千万不能错过的Android NDK下载安装及配置_石子君的博客-CSDN博客_android ndk下载 (38条消息) Android扩展知识 - so文件生成及其使用_L- ...
- js收藏网页功能，纠正网上乱转没求证的案例
网站一般流行以下收藏代码 function AddFavorite(title, url){ try{ //ie收藏 window.external.addFavorite(url, title); ...
- nvm-windows 安装遇到的问题 node目录卸载后（有残留）记得改名
需求 网上好多新项目都需要最新版的node,所有需要切换node版本 nvm-windows https://github.com/coreybutler/nvm-windows 安装步骤-问题 删除 ...
- 动态挂载指定vue组件 Vue.extend $mount('#aaa111')
模板中要有定位 <template> <div id="aaa111"></div> </template> 指定某个函数执行 im ...
- react中css里面 class中的 图片的相对地址 完美解决 backgroundImage
发现问题:缓存 之前react的图片,也在style里面,也无所谓. 刚做了一个输入框,change的时候改变图片,每次都刷新图片,关键是没缓存,这哪受得了 之前用的: 网上搜索各种插件,替换什么的, ...
- Linux int型转换为char*型几种方法总结
一 前记 这种转换,windows下最常用就是atoi()函数.可惜的是,在Linux中没有itoa()函数,只有atoi() 这点很有趣,居然不对称. 所以在Linux中实现从整型到char*的 ...
- Android TextView设置某段文字可点击
初次进入app,需要有个勾选隐私协议的UI,其中的隐私协议文字点击是可跳转到新页面对隐私协议机型展示 这里选择使用Android自带的SpannedString来设置TextView的文字内容即可设置 ...
- C++中fopen的句柄返回NULL
我们在使用fopen打开文件的时候有时会出现失败返回null情况,但是我们不能直接通过log具体是什么原因导致的,所以这时我们可以通过errno和strerror获取错误码和错误信息. 我遇到的是错误 ...
- 聊聊ChatGLM-6B医疗数据微调
转载请注明出处: https://www.cnblogs.com/zhiyong-ITNote/ 参考了多个医疗大模型,如扁鹊.灵心等,重新思考了下微调的方案以及数据集的格式:基于ChatGLM/其它 ...
- 瑞云科技联合飞蝶VR教育、大朋VR推出元宇宙 5G VR智慧教育整体解决方案
近日,瑞云科技3DCAT实时渲染云与飞蝶VR.大朋VR达成深度合作.基于瑞云深度自研的实时渲染云技术.飞蝶VR教育内容资源的深厚积累以及大朋VR优秀的VR硬件产品力,三方针对元宇宙 5G VR智慧教育 ...