Mysql-高级查询语句
2022-06-05 20:42
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Mysql-高级查询语句
本博客中数据来源于：mysql官方练习数据库。
该数据库结构为：
1.控制语句
1.1DISTINCT
distinct用于记录该字段有多少不同的字段。如下所示，title表中第二个字段title有多条重复记录。
使用DISTINCT语句可以方便查询该字段有多少不同的值。
mysql> SELECT distinct title FROM `titles`; +--------------------+ | title | +--------------------+ | Assistant Engineer | | Senior Staff | | Engineer | | Staff | | Technique Leader | | Senior Engineer | | Manager | +--------------------+ 7 rows in set (0.18 sec)
配合count使用，可以计算该列不同值的个数。
mysql> SELECT count(distinct title) FROM `titles`; +-----------------------+ | count(distinct title) | +-----------------------+ | 7 | +-----------------------+ 1 row in set (0.09 sec)
1.2 WHERE
使用where语句可以查看限定条件下的数据。
employees表中记录不同员工的雇佣日期。
通过where语句可以筛选出所有雇佣日期为1986-06-26的雇员
mysql> select * from employees where hire_date = '1986-06-26'; +--------+------------+----------------+-----------------+--------+------------+ | emp_no | birth_date | first_name | last_name | gender | hire_date | +--------+------------+----------------+-----------------+--------+------------+ | 10001 | 1953-09-02 | Georgi | Facello | M | 1986-06-26 | | 21891 | 1960-08-25 | Shuzo | Bernatsky | M | 1986-06-26 | | 27425 | 1958-11-06 | Maik | Gunderson | M | 1986-06-26 | | 29250 | 1952-08-11 | Radoslaw | Besancenot | M | 1986-06-26 | | 32297 | 1955-03-24 | Chandrasekaran | Loncour | M | 1986-06-26 | | 35301 | 1956-01-31 | Basim | Worfolk | F | 1986-06-26 | | 35565 | 1957-12-04 | Chiradeep | Yeung | F | 1986-06-26 | | 41692 | 1961-08-08 | True | Tokunaga | M | 1986-06-26 | ———————————————————————————————————————————————————————————————————————————————— | 478432 | 1962-08-10 | Florian | Beeson | F | 1986-06-26 | | 478983 | 1958-08-21 | Hugo | Litvinov | F | 1986-06-26 | | 483397 | 1956-05-05 | Xuedong | Vanwelkenhuysen | M | 1986-06-26 | | 499666 | 1955-12-03 | Martine | Pollock | M | 1986-06-26 | +--------+------------+----------------+-----------------+--------+------------+ 83 rows in set (0.07 sec)
配合and语句可以筛选出雇佣日期为1986-06-26且性别（gender）为F（女性）的雇员。
mysql> select * from employees where hire_date = '1986-06-26' AND gender = 'F'; +--------+------------+------------+-------------+--------+------------+ | emp_no | birth_date | first_name | last_name | gender | hire_date | +--------+------------+------------+-------------+--------+------------+ | 35301 | 1956-01-31 | Basim | Worfolk | F | 1986-06-26 | | 35565 | 1957-12-04 | Chiradeep | Yeung | F | 1986-06-26 | | 50733 | 1952-06-07 | Hironoby | Nivat | F | 1986-06-26 | | 52077 | 1964-12-14 | Rosella | Streit | F | 1986-06-26 | ———————————————————————————————————————————————————————————————————————— | 458304 | 1963-12-01 | Shuzo | Kirkerud | F | 1986-06-26 | | 464413 | 1964-02-16 | Mart | Lorho | F | 1986-06-26 | | 478432 | 1962-08-10 | Florian | Beeson | F | 1986-06-26 | | 478983 | 1958-08-21 | Hugo | Litvinov | F | 1986-06-26 | +--------+------------+------------+-------------+--------+------------+ 35 rows in set (0.06 sec)
配和or语句可以筛选两个条件符合其中一个的记录。如雇佣日期为1986-06-26或1986-09-17的雇员。
mysql> select * from employees where hire_date = '1986-06-26' or hire_date = '1986-09-17'; +--------+------------+----------------+-----------------+--------+------------+ | emp_no | birth_date | first_name | last_name | gender | hire_date | +--------+------------+----------------+-----------------+--------+------------+ | 10001 | 1953-09-02 | Georgi | Facello | M | 1986-06-26 | | 17761 | 1958-04-19 | Adin | Matheson | F | 1986-09-17 | | 21891 | 1960-08-25 | Shuzo | Bernatsky | M | 1986-06-26 | | 23606 | 1956-06-15 | Theirry | Zirintsis | M | 1986-09-17 | | 23680 | 1962-07-14 | Mary | Navazio | F | 1986-09-17 | ———————————————————————————————————————————————————————————————————————— | 28104 | 1953-08-12 | Dmitry | Marsiglia | F | 1986-09-17 | | 29250 | 1952-08-11 | Radoslaw | Besancenot | M | 1986-06-26 | | 29615 | 1958-12-30 | Atreye | Conry | M | 1986-09-17 | ———————————————————————————————————————————————————————————————————————— | 499666 | 1955-12-03 | Martine | Pollock | M | 1986-06-26 | +--------+------------+----------------+-----------------+--------+------------+ 175 rows in set (0.06 sec)
当需要多个条件同时筛选，可以通过括号将需要同时筛选的条件括起来。下面这个例子则是将雇佣日期为'1986-06-26'且性别为F的员工或雇佣日期为1986-09-17'且性别为M的员工都筛选出来。
mysql> select * from employees where (hire_date = '1986-06-26' AND gender = 'F') OR (hire_date= '1986-09-17' AND gender = 'M'); +--------+------------+-------------+-------------+--------+------------+ | emp_no | birth_date | first_name | last_name | gender | hire_date | +--------+------------+-------------+-------------+--------+------------+ | 23606 | 1956-06-15 | Theirry | Zirintsis | M | 1986-09-17 | | 27972 | 1955-07-22 | Chaosheng | Stanger | M | 1986-09-17 | | 29615 | 1958-12-30 | Atreye | Conry | M | 1986-09-17 | | 32120 | 1962-12-16 | Mingdong | Byoun | M | 1986-09-17 | | 35301 | 1956-01-31 | Basim | Worfolk | F | 1986-06-26 | | 35565 | 1957-12-04 | Chiradeep | Yeung | F | 1986-06-26 | | 37675 | 1955-10-01 | Chikara | Marshall | M | 1986-09-17 | —————————————————————————————————————————————————————————————————————————— | 475938 | 1965-01-14 | Shigeaki | Lanteri | M | 1986-09-17 | | 478432 | 1962-08-10 | Florian | Beeson | F | 1986-06-26 | | 478641 | 1964-05-05 | Pramod | Litvinov | M | 1986-09-17 | | 478983 | 1958-08-21 | Hugo | Litvinov | F | 1986-06-26 | | 481538 | 1963-07-24 | Percy | Szmurlo | M | 1986-09-17 | | 482602 | 1954-06-18 | Aamer | Lagarias | M | 1986-09-17 | | 485137 | 1960-12-09 | Bingning | Krohn | M | 1986-09-17 | | 488143 | 1964-10-26 | Constantine | McClure | M | 1986-09-17 | | 490587 | 1955-10-22 | Janalee | VanScheik | M | 1986-09-17 | | 496210 | 1960-07-02 | Alagu | Szmurlo | M | 1986-09-17 | +--------+------------+-------------+-------------+--------+------------+ 86 rows in set (0.07 sec)
1.3 通配符与like
通过通配符与like可以模糊查询符合需求的记录。如下面这个查询语句可以查找出所有first_name为Chao的员工。
mysql> select * from employees where first_name like 'Chao%'; +--------+------------+------------+------------------+--------+------------+ | emp_no | birth_date | first_name | last_name | gender | hire_date | +--------+------------+------------+------------------+--------+------------+ | 11829 | 1952-08-01 | Chaosheng | Pettis | F | 1999-02-17 | | 12923 | 1953-09-05 | Chaosheng | Journel | F | 1990-01-02 | | 13524 | 1955-11-06 | Chaoyi | Porotnikoff | F | 1985-07-27 | | 15343 | 1955-05-21 | Chaosheng | Luce | F | 1985-03-12 | | 16019 | 1955-11-30 | Chaoyi | Heystek | F | 1985-08-01 | —————————————————————————————————————————————————————————————————————————— | 497563 | 1957-10-29 | Chaoyi | Manders | M | 1990-12-02 | | 497796 | 1953-10-15 | Chaoyi | Kushnir | M | 1988-07-19 | | 498761 | 1958-10-09 | Chaoyi | Kaiserswerth | M | 1986-01-01 | | 498894 | 1955-02-10 | Chaoyi | Bahr | F | 1986-09-21 | | 499450 | 1963-04-23 | Chaosheng | Pargaonkar | F | 1988-07-13 | | 499876 | 1959-03-19 | Chaosheng | Orlowska | M | 1988-02-20 | +--------+------------+------------+------------------+--------+------------+ 452 rows in set (0.05 sec)
百分号%代表零或多个字符，而下划线_代表一个字符。
常见的通配符使用方法如下。
- A_Z :A与Z之间有一个字符
- ABC% :以ABC开头的字符串后有零或多个字符
- %XYZ :以XYZ结尾的字符串，前有零或多个字符
- %AN%:AN的前后有零或多个字符
- _AN%:AN前有一个字符，AN后有零或多个字符
1.4 ORDER BY
ORDER BY 用于对字段的排序，默认是升序。如使用order by语句对员工的生日进行升序排序。（出生早的在前面）
mysql> select * from employees order by birth_date limit 100; +--------+------------+------------+--------------+--------+------------+ | emp_no | birth_date | first_name | last_name | gender | hire_date | +--------+------------+------------+--------------+--------+------------+ | 406121 | 1952-02-01 | Supot | Remmele | M | 1989-01-27 | | 91374 | 1952-02-01 | Eishiro | Kuzuoka | M | 1992-02-12 | —————————————————————————————————————————————————————————————————————————— | 87461 | 1952-02-01 | Moni | Decaestecker | M | 1986-10-06 | | 207658 | 1952-02-01 | Kiyokazu | Whitcomb | M | 1988-07-26 | | 498106 | 1952-02-02 | Shai | Calkin | M | 1990-12-02 | | 405962 | 1952-02-02 | Moto | Staudhammer | M | 1995-02-20 | | 409040 | 1952-02-02 | Mayuko | Pardalos | M | 1991-07-03 | | 94615 | 1952-02-02 | Toshimi | Bruckman | M | 1989-04-29 | | 93928 | 1952-02-02 | Tomoyuki | Axelband | F | 1987-09-08 | | 244265 | 1952-02-02 | Pantung | Halevi | M | 1993-11-12 | —————————————————————————————————————————————————————————————————————————— | 239891 | 1952-02-02 | Percy | Tischendorf | M | 1986-11-10 | | 455745 | 1952-02-02 | Moni | Giveon | F | 1994-01-17 | | 462774 | 1952-02-02 | Moie | Chinal | F | 1997-09-20 | | 203054 | 1952-02-02 | Hausi | Krohn | M | 1994-11-23 | | 463921 | 1952-02-02 | Lalit | Bahr | M | 1987-05-27 | | 469911 | 1952-02-02 | Mizuhito | Szemeredi | F | 1990-02-24 | | 107344 | 1952-02-02 | Kiyomitsu | Gelosh | F | 1989-12-03 | | 206240 | 1952-02-03 | Oksana | Zykh | M | 1988-03-22 | | 406833 | 1952-02-03 | Aiichiro | Kobuchi | M | 1990-11-23 | | 70603 | 1952-02-03 | Otilia | Parhami | M | 1991-01-28 | | 61129 | 1952-02-03 | Rildo | Bain | M | 1992-04-03 | —————————————————————————————————————————————————————————————————————————— | 93975 | 1952-02-03 | Gererd | Calkin | M | 1988-04-18 | | 221356 | 1952-02-03 | Pradeep | Hagimont | M | 1987-09-24 | | 294298 | 1952-02-03 | Vesna | Coney | M | 1999-06-28 | +--------+------------+------------+--------------+--------+------------+ 100 rows in set (0.07 sec)
使用DESC则为倒序排序。
mysql> select * from employees order by birth_date DESC limit 100; +--------+------------+----------------+-----------------+--------+------------+ | emp_no | birth_date | first_name | last_name | gender | hire_date | +--------+------------+----------------+-----------------+--------+------------+ | 457832 | 1965-02-01 | Jackson | Zielinski | F | 1985-04-04 | | 424584 | 1965-02-01 | Kagan | Dredge | M | 1994-02-26 | —————————————————————————————————————————————————————————————————————————— | 284045 | 1965-02-01 | Fun | Seiwald | M | 1994-06-24 | | 294996 | 1965-02-01 | Tomoyuki | Vigier | F | 1991-07-08 | | 437369 | 1965-02-01 | Kazuhide | Biran | F | 1995-01-25 | | 93278 | 1965-02-01 | Magdalena | Penn | F | 1987-04-27 | | 418860 | 1965-02-01 | Ymte | Dalton | F | 1992-11-22 | | 109598 | 1965-02-01 | Stamatina | Auyong | M | 1988-07-05 | | 40785 | 1965-01-31 | Youpyo | Castellani | M | 1998-09-04 | | 97661 | 1965-01-31 | Avishai | Hegner | M | 1993-05-08 | —————————————————————————————————————————————————————————————————————————— | 235269 | 1965-01-31 | Keiichiro | Feldmann | F | 1989-06-28 | | 37719 | 1965-01-31 | Nakhoon | Buescher | M | 1986-07-28 | | 52770 | 1965-01-31 | Shugo | Yurek | M | 1986-01-06 | +--------+------------+----------------+-----------------+--------+------------+ 100 rows in set (0.07 sec)
2.函数
2.1 数学函数
数学函数主要是对数字的处理。
现有这样一张表（自建）
mysql> select * from test_math; +------+------+------+ | num1 | num2 | num3 | +------+------+------+ | 15 | 20 | 30 | | 17 | 10 | 3 | | -2 | 10 | 25 | +------+------+------+ 3 rows in set (0.01 sec)
函数**abs()**返回该字段的绝对值。
mysql> select abs(num1) from test_math; +-----------+ | abs(num1) | +-----------+ | 15 | | 17 | | 2 | +-----------+ 3 rows in set (0.00 sec)
函数**rand ()**返回0-1的随机值。
mysql> select rand(); +--------------------+ | rand() | +--------------------+ | 0.5209844825053443 | +--------------------+ 1 row in set (0.00 sec)
函数**mod(x,y)**返回x/y的余数。
mysql> select num1,num2,mod(num1,num2) from test_math; +------+------+----------------+ | num1 | num2 | mod(num1,num2) | +------+------+----------------+ | 15 | 20 | 15 | | 17 | 10 | 7 | | -2 | 10 | -2 | +------+------+----------------+ 3 rows in set (0.00 sec)
函数**power (x,y)**返回x的y次方(第一行e23,代表10的23次方，由于数字过大，采用了科学计数法)
mysql> select num1,num2,power(num1,num2) from test_math; +------+------+-----------------------+ | num1 | num2 | power(num1,num2) | +------+------+-----------------------+ | 15 | 20 | 3.3252567300796506e23 | | 17 | 10 | 2015993900449 | | -2 | 10 | 1024 | +------+------+-----------------------+ 3 rows in set (0.00 sec)
函数**greatest (xl,x2. . .)**返回集合中的最大数。
mysql> select num1,num2,num3,greatest(num1,num2,num3) from test_math; +------+------+------+--------------------------+ | num1 | num2 | num3 | greatest(num1,num2,num3) | +------+------+------+--------------------------+ | 15 | 20 | 30 | 30 | | 17 | 10 | 3 | 17 | | -2 | 10 | 25 | 25 | +------+------+------+--------------------------+ 3 rows in set (0.00 sec)
函数**least (xl,x2. . .)**返回集合中的最小数。
mysql> select num1,num2,num3,least(num1,num2,num3) from test_math; +------+------+------+-----------------------+ | num1 | num2 | num3 | least(num1,num2,num3) | +------+------+------+-----------------------+ | 15 | 20 | 30 | 15 | | 17 | 10 | 3 | 3 | | -2 | 10 | 25 | -2 | +------+------+------+-----------------------+ 3 rows in set (0.00 sec)
其余常用的数学函数还有：
round (X)
返回离x最近的整数
round(x, y)
保留x的y位小数四舍五入后的值
sqrt(x)
返回x的平方根
truncate (x, y)
返回数字x截断为y位小数的值
ceil (x)
返回大于或等于x的最小整数
floor (x)
返回小于或等于x的最大整数
2.2 聚合函数
主要涉及对字段数据的处理，依旧使用test_math进行演示。
mysql> select * from test_math; +------+------+------+ | num1 | num2 | num3 | +------+------+------+ | 15 | 20 | 30 | | 17 | 10 | 3 | | -2 | 10 | 25 | +------+------+------+ 3 rows in set (0.01 sec)
函数**avg ()**求指定列的平均值
mysql> select AVG(num3) from test_math; +-----------+ | AVG(num3) | +-----------+ | 19.3333 | +-----------+ 1 row in set (0.00 sec)
函数**min()**求指定列的最小值
mysql> select min(num3) from test_math; +-----------+ | min(num3) | +-----------+ | 3 | +-----------+ 1 row in set (0.00 sec)
函数**MAX()**求指定列的最大值
mysql> select max(num3) from test_math; +-----------+ | max(num3) | +-----------+ | 30 | +-----------+ 1 row in set (0.00 sec)
函数**sum (x)**返回指定列的和
mysql> select sum(num3) from test_math; +-----------+ | sum(num3) | +-----------+ | 58 | +-----------+ 1 row in set (0.00 sec)
2.3 字符串函数
字符串函数顾名思义就是针对字符串进行处理的函数
现有表
mysql> select * from test_char; +-------+-------+----------------+ | char1 | char2 | char3 | +-------+-------+----------------+ | KY | 02 | zengguoqiang | | KY | 11 | changzeyou | | CT | 83 | wudifenghuolun | +-------+-------+----------------+ 3 rows in set (0.00 sec)
函数**concat (x, y)**将x和y拼接为一个字符，xy可以是字段，也可以是符号
mysql> select char1,char2,concat(char1,char2),concat('2022-',char1) from test_char;
+-------+-------+---------------------+-----------------------+
| char1 | char2 | concat(char1,char2) | concat('2022-',char1) |
+-------+-------+---------------------+-----------------------+
| KY | 02 | KY02 | 2022-KY |
| KY | 11 | KY11 | 2022-KY |
| CT | 83 | CT83 | 2022-CT |
+-------+-------+---------------------+-----------------------+
3 rows in set (0.00 sec)
函数**substr (x,y, z)**用于截取字符串，x代表字段，y代表截取位置，z代表截取长度。
mysql> select char3,substr(char3,2,4) from test_char; +----------------+-------------------+ | char3 | substr(char3,2,4) | +----------------+-------------------+ | zengguoqiang | engg | | changzeyou | hang | | wudifenghuolun | udif | +----------------+-------------------+ 3 rows in set (0.00 sec)
函数**length (x)**可以获取字符串长度。
mysql> select char3,length(char3) from test_char; +----------------+---------------+ | char3 | length(char3) | +----------------+---------------+ | zengguoqiang | 12 | | changzeyou | 10 | | wudifenghuolun | 14 | +----------------+---------------+ 3 rows in set (0.00 sec)
函数**replace(x, y, z)**用于替换字符串内容，x代表被替换的字符串，y代表被替换的内容，z代表替换的内容。这三个可以是字符串也可是字段名称。
mysql> select *,replace(char3,'uo',char2) from test_char; +-------+-------+----------------+---------------------------+ | char1 | char2 | char3 | replace(char3,'uo',char2) | +-------+-------+----------------+---------------------------+ | KY | 02 | zengguoqiang | zengg02qiang | | KY | 11 | changzeyou | changzeyou | | CT | 83 | wudifenghuolun | wudifengh83lun | +-------+-------+----------------+---------------------------+ 3 rows in set (0.00 sec
其余常用字符串函数还有:
upper (x)
将字符串x的所有字母变成大写字母
lower (x)
将字符串x的所有字母变成小写字母
left(x,y)
返回字符串x的前y个字符
right (x,y)
返回字符串x的后y个字符
repeat (x, y)
将字符串x重复y次
space (x)
返回x个空格
3. 连接（join）
mysql在涉及多表关联字段查询的时候可以通过join来实现指定内容的查找，mysql连接种类大致分为：
- INNER JOIN（内连接,或等值连接）：获取两个表中字段匹配关系的记录。
- **LEFT JOIN（左连接）：**获取左表所有记录，即使右表没有对应匹配的记录。
- RIGHT JOIN（右连接）： 与 LEFT JOIN 相反，用于获取右表所有记录，即使左表没有对应匹配的记录。
现有两表
mysql> select * from LEFT_tb1; +--------+----------+ | ssh_id | ssh_name | +--------+----------+ | 1 | zhangsan | | 2 | lisi | | 3 | yefan | | 7 | admin | +--------+----------+ 4 rows in set (0.00 sec) mysql> select * from RIGHT_tb; +--------+-----------+---------------+------------+ | ssh_id | ssh_count | ssh_ip | last_log | +--------+-----------+---------------+------------+ | 1 | 20 | 192.168.80.30 | 2022-06-04 | | 2 | 33 | 192.168.80.50 | 2022-05-10 | | 3 | 45 | 192.168.80.20 | 2022-05-25 | | 4 | 12 | 192.168.80.11 | 2022-05-03 | | 5 | 1 | 100.0.0.1 | 2022-04-26 | +--------+-----------+---------------+------------+ 5 rows in set (0.00 sec)
3.1 INNER JOIN（内连接)
通过INNER JOIN可以查看表LEFT_tb1与RIGHT_tb关联字段ssh_id的对应记录。
mysql> select l.ssh_id,l.ssh_name,r.ssh_count,r.ssh_ip,r.last_log from LEFT_tb1 l INNER JOIN RIGHT_tb r on l.ssh_id = r.ssh_id; +--------+----------+-----------+---------------+------------+ | ssh_id | ssh_name | ssh_count | ssh_ip | last_log | +--------+----------+-----------+---------------+------------+ | 1 | zhangsan | 20 | 192.168.80.30 | 2022-06-04 | | 2 | lisi | 33 | 192.168.80.50 | 2022-05-10 | | 3 | yefan | 45 | 192.168.80.20 | 2022-05-25 | +--------+----------+-----------+---------------+------------+ 3 rows in set (0.00 sec)
INNER JOIN关系类似于上图，只获取交叉数据。
3.2 LEFT JOIN（左连接）
MySQL left join 与 join 有所不同。 MySQL LEFT JOIN 会读取左边数据表的全部数据，即便右边表无对应数据。无对应数据字段用NULL填充。
mysql> select l.ssh_id,l.ssh_name,r.ssh_count,r.ssh_ip,r.last_log from LEFT_tb1 l LEFT JOIN RIGHT_tb r on l.ssh_iid = r.ssh_id; +--------+----------+-----------+---------------+------------+ | ssh_id | ssh_name | ssh_count | ssh_ip | last_log | +--------+----------+-----------+---------------+------------+ | 1 | zhangsan | 20 | 192.168.80.30 | 2022-06-04 | | 2 | lisi | 33 | 192.168.80.50 | 2022-05-10 | | 3 | yefan | 45 | 192.168.80.20 | 2022-05-25 | | 7 | admin | NULL | NULL | NULL | +--------+----------+-----------+---------------+------------+ 4 rows in set (0.00 sec)
3.3 RIGHT JOIN（右连接）
MySQL RIGHT JOIN 会读取右边数据表的全部数据，即便左边边表无对应数据。
mysql> select l.ssh_id,l.ssh_name,r.ssh_count,r.ssh_ip,r.last_log from LEFT_tb1 l RIGHT JOIN RIGHT_tb r on l.ssh__id = r.ssh_id; +--------+----------+-----------+---------------+------------+ | ssh_id | ssh_name | ssh_count | ssh_ip | last_log | +--------+----------+-----------+---------------+------------+ | 1 | zhangsan | 20 | 192.168.80.30 | 2022-06-04 | | 2 | lisi | 33 | 192.168.80.50 | 2022-05-10 | | 3 | yefan | 45 | 192.168.80.20 | 2022-05-25 | | NULL | NULL | 12 | 192.168.80.11 | 2022-05-03 | | NULL | NULL | 1 | 100.0.0.1 | 2022-04-26 | +--------+----------+-----------+---------------+------------+ 5 rows in set (0.00 sec)
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