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mysql8学习笔记13--常用函数（一）

操作符优先级

• 下图展示了所有操作符的执行优先级，从高到低，同一行中的操作符优先级相同，相同优先级的情况下则从左到右执行

• 如果想改变优先级执行顺序，则可以使用括号

mysql> select 1+2*3;
+-------+
| 1+2*3 |
+-------+
|     7 |
+-------+
1 row in set (0.00 sec)

mysql> select (1+1)*3;
+---------+
| (1+1)*3 |
+---------+
|       6 |
+---------+
1 row in set (0.00 sec)

mysql>

对比操作符

• 对比操作符的执行结果为true,false,null三种

• Between A and B 代表检查值是否在A和B之间

• Coalesce()代表返回第一个非Null的值

• =代表相等操作符

• >代表大于操作符

• >=代表大于等于操作符

• Greatest()代表返回最大的值

• In()代表检查值是否在一系列的值之中

• Interval()代表返回比第一个参数小的参数的位置

• is/is not代表检查值是否与布尔值相同/不同

• Is not null代表检查值是否是非NULL

• Is null代表检查值是否是NULL

•isnull(exper) 判断exper是否为NULL，是则返回1，否则返回0

• ifnull(exper1,exper2)判断exper1是否为空，是则用exper2代替

• nullif(exper1,exper2)如果expr1= expr2 成立，那么返回值为NULL，否则返回值为 expr1

• Least()代表返回最小的参数

• <代表小于操作符

• <=代表小于等于操作符

• Like代表字符匹配

• Not between A and B代表检查值是否不在A和B的范围之内

• !=/<>代表不等于操作符

• Not in()代表检查值是否不在一系列值的当中

• Not like代表检查值是否不匹配

• Strcmp()对比两个字符串

mysql> select * from customers3;
+---------+----------------+---------------------+-----------+------------+----------+--------------+--------------+---------------------+
| cust_id | cust_name      | cust_address        | cust_city | cust_state | cust_zip | cust_country | cust_contact | cust_email          |
+---------+----------------+---------------------+-----------+------------+----------+--------------+--------------+---------------------+
|   10001 | Coyote Inc.    | 200 Maple Lane      | Detroit   | MI         | 44444    | USA          | Y Lee        | ylee@coyote.com     |
|   10002 | Mouse House    | 333 Fromage Lane    | Columbus  | OH         | 43333    | USA          | Jerry Mouse  | NULL                |
|   10003 | Wascals        | 1 Sunny Place       | Muncie    | IN         | 42222    | USA          | Jim Jones    | rabbit@wascally.com |
|   10004 | Yosemite Place | 829 Riverside Drive | Phoenix   | AZ         | 88888    | USA          | Y Sam        | sam@yosemite.com    |
|   10005 | E Fudd         | 4545 53rd Street    | Chicago   | IL         | 54545    | USA          | E Fudd       | NULL                |
+---------+----------------+---------------------+-----------+------------+----------+--------------+--------------+---------------------+
5 rows in set (0.00 sec)

mysql> select * from customers3 where cust_id between 10001 and 10003;#Between A and B 代表检查值是否在A和B之间
+---------+-------------+------------------+-----------+------------+----------+--------------+--------------+---------------------+
| cust_id | cust_name   | cust_address     | cust_city | cust_state | cust_zip | cust_country | cust_contact | cust_email          |
+---------+-------------+------------------+-----------+------------+----------+--------------+--------------+---------------------+
|   10001 | Coyote Inc. | 200 Maple Lane   | Detroit   | MI         | 44444    | USA          | Y Lee        | ylee@coyote.com     |
|   10002 | Mouse House | 333 Fromage Lane | Columbus  | OH         | 43333    | USA          | Jerry Mouse  | NULL                |
|   10003 | Wascals     | 1 Sunny Place    | Muncie    | IN         | 42222    | USA          | Jim Jones    | rabbit@wascally.com |
+---------+-------------+------------------+-----------+------------+----------+--------------+--------------+---------------------+
3 rows in set (0.00 sec)

mysql> select coalesce(null,2,3,1);#Coalesce()代表返回第一个非Null的值
+----------------------+
| coalesce(null,2,3,1) |
+----------------------+
|                    2 |
+----------------------+
1 row in set (0.00 sec)
mysql> alter table customers3 add column cust_start varchar(20) default null;
Query OK, 0 rows affected (0.09 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> select * from customers3 where cust_id between 10001 and 10004;
+---------+----------------+---------------------+-----------+------------+----------+--------------+--------------+---------------------+------------+
| cust_id | cust_name      | cust_address        | cust_city | cust_state | cust_zip | cust_country | cust_contact | cust_email          | cust_start |
+---------+----------------+---------------------+-----------+------------+----------+--------------+--------------+---------------------+------------+
|   10001 | Coyote Inc.    | 200 Maple Lane      | Detroit   | MI         | 44444    | USA          | Y Lee        | ylee@coyote.com     | NULL       |
|   10002 | Mouse House    | 333 Fromage Lane    | Columbus  | OH         | 43333    | USA          | Jerry Mouse  | NULL                | NULL       |
|   10003 | Wascals        | 1 Sunny Place       | Muncie    | IN         | 42222    | USA          | Jim Jones    | rabbit@wascally.com | NULL       |
|   10004 | Yosemite Place | 829 Riverside Drive | Phoenix   | AZ         | 88888    | USA          | Y Sam        | sam@yosemite.com    | NULL       |
+---------+----------------+---------------------+-----------+------------+----------+--------------+--------------+---------------------+------------+
4 rows in set (0.00 sec)

mysql> select coalesce(cust_start,1) as cust_start from customers3;;#Coalesce()代表返回第一个非Null的值,这个参数使用的场合为：假如某个字段默认是null，你想其返回的不是null，而是比如0或其他值，可以使用这个函数
+------------+
| cust_start |
+------------+
| 1          |
| 1          |
| 1          |
| 1          |
| 1          |
+------------+
5 rows in set (0.00 sec)

ERROR: 
No query specified

mysql>

mysql> select * from customers3;
+---------+----------------+---------------------+-----------+------------+----------+--------------+--------------+---------------------+------------+
| cust_id | cust_name      | cust_address        | cust_city | cust_state | cust_zip | cust_country | cust_contact | cust_email          | cust_start |
+---------+----------------+---------------------+-----------+------------+----------+--------------+--------------+---------------------+------------+
|   10001 | Coyote Inc.    | 200 Maple Lane      | Detroit   | MI         | 44444    | USA          | Y Lee        | ylee@coyote.com     | NULL       |
|   10002 | Mouse House    | 333 Fromage Lane    | Columbus  | OH         | 43333    | USA          | Jerry Mouse  | NULL                | NULL       |
|   10003 | Wascals        | 1 Sunny Place       | Muncie    | IN         | 42222    | USA          | Jim Jones    | rabbit@wascally.com | NULL       |
|   10004 | Yosemite Place | 829 Riverside Drive | Phoenix   | AZ         | 88888    | USA          | Y Sam        | sam@yosemite.com    | NULL       |
|   10005 | E Fudd         | 4545 53rd Street    | Chicago   | IL         | 54545    | USA          | E Fudd       | NULL                | NULL       |
+---------+----------------+---------------------+-----------+------------+----------+--------------+--------------+---------------------+------------+
5 rows in set (0.00 sec)

mysql> select greatest(cust_id,cust_zip,cust_start) from customers3;#Greatest()代表返回最大的值,当字段有值是null时，返回null
+---------------------------------------+
| greatest(cust_id,cust_zip,cust_start) |
+---------------------------------------+
| NULL                                  |
| NULL                                  |
| NULL                                  |
| NULL                                  |
| NULL                                  |
+---------------------------------------+
5 rows in set (0.00 sec)

mysql> select greatest(cust_id,cust_zip) from customers3;
+----------------------------+
| greatest(cust_id,cust_zip) |
+----------------------------+
| 44444                      |
| 43333                      |
| 42222                      |
| 88888                      |
| 54545                      |
+----------------------------+
5 rows in set (0.00 sec)

mysql>

mysql> show tables;
+------------------+
| Tables_in_school |
+------------------+
| tb_college       |
| tb_course        |
| tb_score         |
| tb_student       |
| tb_teacher       |
+------------------+
5 rows in set (0.01 sec)

mysql> select * from tb_student;
+-------+--------------+--------+------------+--------------+--------+
| stuid | stuname      | stusex | stubirth   | stuaddr      | collid |
+-------+--------------+--------+------------+--------------+--------+
|  1001 | 杨逍         |       | 1990-03-04 | 四川成都     |      1 |
|  1002 | 任我行       |       | 1992-02-02 | 湖南长沙     |      1 |
|  1033 | 王语嫣       |        | 1989-12-03 | 四川成都     |      1 |
|  1378 | 纪嫣然       |        | 1995-08-12 | 四川绵阳     |      1 |
|  1572 | 岳不群       |       | 1993-07-19 | 陕西咸阳     |      1 |
|  1954 | 林平之       |       | 1994-09-20 | 福建莆田     |      1 |
|  2035 | 东方不败     |       | 1988-06-30 | NULL         |      2 |
|  3011 | 林震南       |       | 1985-12-12 | 福建莆田     |      3 |
|  3755 | 项少龙       |       | 1993-01-25 | NULL         |      3 |
|  3923 | 杨不悔       |        | 1985-04-17 | 四川成都     |      3 |
+-------+--------------+--------+------------+--------------+--------+
10 rows in set (0.01 sec)

mysql> select * from tb_student where stuid between 1002 and 1378;
+-------+-----------+--------+------------+--------------+--------+
| stuid | stuname   | stusex | stubirth   | stuaddr      | collid |
+-------+-----------+--------+------------+--------------+--------+
|  1002 | 任我行    |       | 1992-02-02 | 湖南长沙     |      1 |
|  1033 | 王语嫣    |        | 1989-12-03 | 四川成都     |      1 |
|  1378 | 纪嫣然    |        | 1995-08-12 | 四川绵阳     |      1 |
+-------+-----------+--------+------------+--------------+--------+
3 rows in set (0.00 sec)

mysql> select coalesce(null,2,3,1);
+----------------------+
| coalesce(null,2,3,1) |
+----------------------+
|                    2 |
+----------------------+
1 row in set (0.00 sec)

mysql> select coalesce(stuaddr,2),stuid,stuaddr from tb_student where stuid=2035; #Coalesce()代表返回第一个非Null的值,这个参数使用的场合为：假如某个字段默认是null，你想其返回的不是null，而是比如0或其他值，可以使用这个函数
+---------------------+-------+---------+
| coalesce(stuaddr,2) | stuid | stuaddr |
+---------------------+-------+---------+
| 2                   |  2035 | NULL    |
+---------------------+-------+---------+
1 row in set (0.00 sec)

mysql> 
mysql> select * from tb_student where stuid=1002;
+-------+-----------+--------+------------+--------------+--------+
| stuid | stuname   | stusex | stubirth   | stuaddr      | collid |
+-------+-----------+--------+------------+--------------+--------+
|  1002 | 任我行    |       | 1992-02-02 | 湖南长沙     |      1 |
+-------+-----------+--------+------------+--------------+--------+
1 row in set (0.00 sec)

mysql> select * from tb_student where stuid>=1002 and stuid<=1378;
+-------+-----------+--------+------------+--------------+--------+
| stuid | stuname   | stusex | stubirth   | stuaddr      | collid |
+-------+-----------+--------+------------+--------------+--------+
|  1002 | 任我行    |       | 1992-02-02 | 湖南长沙     |      1 |
|  1033 | 王语嫣    |        | 1989-12-03 | 四川成都     |      1 |
|  1378 | 纪嫣然    |        | 1995-08-12 | 四川绵阳     |      1 |
+-------+-----------+--------+------------+--------------+--------+
3 rows in set (0.00 sec)

mysql> 
mysql> select * from tb_course;
+-------+-----------------------+-----------+-------+
| couid | couname               | coucredit | teaid |
+-------+-----------------------+-----------+-------+
|  1111 | Python程序设计        |         3 |  1122 |
|  2222 | Web前端开发           |         2 |  1122 |
|  3333 | 操作系统              |         4 |  1122 |
|  4444 | 计算机网络            |         2 |  1133 |
|  5555 | 编译原理              |         4 |  1144 |
|  6666 | 算法和数据结构        |         3 |  1144 |
|  7777 | 经贸法语              |         3 |  2255 |
|  8888 | 成本会计              |         2 |  3366 |
|  9999 | 审计学                |         3 |  3366 |
+-------+-----------------------+-----------+-------+
9 rows in set (0.00 sec)

mysql> desc tb_course;
+-----------+-------------+------+-----+---------+-------+
| Field     | Type        | Null | Key | Default | Extra |
+-----------+-------------+------+-----+---------+-------+
| couid     | int(11)     | NO   | PRI | NULL    |       |
| couname   | varchar(50) | NO   |     | NULL    |       |
| coucredit | int(11)     | NO   |     | NULL    |       |
| teaid     | int(11)     | NO   | MUL | NULL    |       |
+-----------+-------------+------+-----+---------+-------+
4 rows in set (0.00 sec)
mysql> select greatest(couid,coucredit,teaid) from tb_course; #greatest是横向的，取每条记录的最大值。
+---------------------------------+
| greatest(couid,coucredit,teaid) |
+---------------------------------+
|                            1122 |
|                            2222 |
|                            3333 |
|                            4444 |
|                            5555 |
|                            6666 |
|                            7777 |
|                            8888 |
|                            9999 |
+---------------------------------+
9 rows in set (0.01 sec)

mysql> 
mysql> select max(couid) from tb_course; #max是纵向的
+------------+
| max(couid) |
+------------+
|       9999 |
+------------+
1 row in set (0.00 sec)

mysql> 
mysql> select * from tb_student where stuid in (1001,3923); #In()代表检查值是否在一系列的值之中
+-------+-----------+--------+------------+--------------+--------+
| stuid | stuname   | stusex | stubirth   | stuaddr      | collid |
+-------+-----------+--------+------------+--------------+--------+
|  1001 | 杨逍      |       | 1990-03-04 | 四川成都     |      1 |
|  3923 | 杨不悔    |        | 1985-04-17 | 四川成都     |      3 |
+-------+-----------+--------+------------+--------------+--------+
2 rows in set (0.00 sec)

mysql> select * from tb_student where stuid in (1001);
+-------+---------+--------+------------+--------------+--------+
| stuid | stuname | stusex | stubirth   | stuaddr      | collid |
+-------+---------+--------+------------+--------------+--------+
|  1001 | 杨逍    |       | 1990-03-04 | 四川成都     |      1 |
+-------+---------+--------+------------+--------------+--------+
1 row in set (0.00 sec)

mysql> select * from tb_student where stuid in ();#
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ')' at line 1
mysql> 

mysql> select interval(5,1,2,3,4,5,6,7);#INTERVAL()函数进行比较列表(N，N1，N2，N3等等)中的N值。该函数如果N<N1返回0，如果N<N2返回1，如果N<N3返回2 等等。如果N为NULL，它将返回-1。列表值必须是N1<N2<N3的形式才能正常工作。
+---------------------------+
| interval(5,1,2,3,4,5,6,7) |
+---------------------------+
|                         5 |
+---------------------------+
1 row in set (0.00 sec)

mysql> select interval(null,1,2,3,4,5,6,7);
+------------------------------+
| interval(null,1,2,3,4,5,6,7) |
+------------------------------+
|                           -1 |
+------------------------------+
1 row in set (0.00 sec)

mysql> select interval(1,1,2,3,4,5,6,7);
+---------------------------+
| interval(1,1,2,3,4,5,6,7) |
+---------------------------+
|                         1 |
+---------------------------+
1 row in set (0.00 sec)

mysql> select interval(0,1,2,3,4,5,6,7);
+---------------------------+
| interval(0,1,2,3,4,5,6,7) |
+---------------------------+
|                         0 |
+---------------------------+
1 row in set (0.00 sec)

mysql> 
mysql> select * from tb_student where stuaddr is  true;#代表检查值是否与布尔值相同/不同
Empty set, 8 warnings (0.00 sec)

mysql> select * from tb_student where stuaddr is  not true;
+-------+--------------+--------+------------+--------------+--------+
| stuid | stuname      | stusex | stubirth   | stuaddr      | collid |
+-------+--------------+--------+------------+--------------+--------+
|  1001 | 杨逍         |       | 1990-03-04 | 四川成都     |      1 |
|  1002 | 任我行       |       | 1992-02-02 | 湖南长沙     |      1 |
|  1033 | 王语嫣       |        | 1989-12-03 | 四川成都     |      1 |
|  1378 | 纪嫣然       |        | 1995-08-12 | 四川绵阳     |      1 |
|  1572 | 岳不群       |       | 1993-07-19 | 陕西咸阳     |      1 |
|  1954 | 林平之       |       | 1994-09-20 | 福建莆田     |      1 |
|  2035 | 东方不败     |       | 1988-06-30 | NULL         |      2 |
|  3011 | 林震南       |       | 1985-12-12 | 福建莆田     |      3 |
|  3755 | 项少龙       |       | 1993-01-25 | NULL         |      3 |
|  3923 | 杨不悔       |        | 1985-04-17 | 四川成都     |      3 |
+-------+--------------+--------+------------+--------------+--------+
10 rows in set, 8 warnings (0.00 sec)

mysql> select * from tb_student where stuaddr = NULL;
Empty set (0.00 sec)

mysql> select * from tb_student where stuaddr is NULL;#Is null代表检查值是否是NULL
+-------+--------------+--------+------------+---------+--------+
| stuid | stuname      | stusex | stubirth   | stuaddr | collid |
+-------+--------------+--------+------------+---------+--------+
|  2035 | 东方不败     |       | 1988-06-30 | NULL    |      2 |
|  3755 | 项少龙       |       | 1993-01-25 | NULL    |      3 |
+-------+--------------+--------+------------+---------+--------+
2 rows in set (0.00 sec)

mysql>
mysql> select * from tb_student where stuaddr is not NULL; #Is not null代表检查值是否是非NULL
+-------+-----------+--------+------------+--------------+--------+
| stuid | stuname   | stusex | stubirth   | stuaddr      | collid |
+-------+-----------+--------+------------+--------------+--------+
|  1001 | 杨逍      |       | 1990-03-04 | 四川成都     |      1 |
|  1002 | 任我行    |       | 1992-02-02 | 湖南长沙     |      1 |
|  1033 | 王语嫣    |        | 1989-12-03 | 四川成都     |      1 |
|  1378 | 纪嫣然    |        | 1995-08-12 | 四川绵阳     |      1 |
|  1572 | 岳不群    |       | 1993-07-19 | 陕西咸阳     |      1 |
|  1954 | 林平之    |       | 1994-09-20 | 福建莆田     |      1 |
|  3011 | 林震南    |       | 1985-12-12 | 福建莆田     |      3 |
|  3923 | 杨不悔    |        | 1985-04-17 | 四川成都     |      3 |
+-------+-----------+--------+------------+--------------+--------+
8 rows in set (0.00 sec)

mysql> 
mysql> select * from tb_course;
+-------+-----------------------+-----------+-------+
| couid | couname               | coucredit | teaid |
+-------+-----------------------+-----------+-------+
|  1111 | Python程序设计        |         3 |  1122 |
|  2222 | Web前端开发           |         2 |  1122 |
|  3333 | 操作系统              |         4 |  1122 |
|  4444 | 计算机网络            |         2 |  1133 |
|  5555 | 编译原理              |         4 |  1144 |
|  6666 | 算法和数据结构        |         3 |  1144 |
|  7777 | 经贸法语              |         3 |  2255 |
|  8888 | 成本会计              |         2 |  3366 |
|  9999 | 审计学                |         3 |  3366 |
+-------+-----------------------+-----------+-------+
9 rows in set (0.00 sec)
#isnull()
mysql> select concat('该专业存在，可以选择') as resp_msg,isnull(t.couname) as result,t.couid from tb_course t where t.couname='Python程序设计';#这个例子举的有点不实用，生产会有用到的场景。
+--------------------------------+--------+-------+
| resp_msg                       | result | couid |
+--------------------------------+--------+-------+
| 该专业存在，可以选择           |      0 |  1111 |
+--------------------------------+--------+-------+
1 row in set (0.00 sec)

mysql> select isnull(1);#isnull(exper) 判断exper是否为NULL，是则返回1，否则返回0
+-----------+
| isnull(1) |
+-----------+
|         0 |
+-----------+
1 row in set (0.00 sec)

mysql> select isnull(null);
+--------------+
| isnull(null) |
+--------------+
|            1 |
+--------------+
1 row in set (0.00 sec)

mysql> select ifnull(null,3);# ifnull(exper1,exper2)判断exper1是否为空，是则用exper2代替
+----------------+
| ifnull(null,3) |
+----------------+
|              3 |
+----------------+
1 row in set (0.00 sec)

mysql> select ifnull(2,3);
+-------------+
| ifnull(2,3) |
+-------------+
|           2 |
+-------------+
1 row in set (0.00 sec)

mysql> 

mysql> select nullif(2,2);# nullif(exper1,exper2)如果expr1= expr2 成立，那么返回值为NULL，否则返回值为   expr1
+-------------+
| nullif(2,2) |
+-------------+
|        NULL |
+-------------+
1 row in set (0.00 sec)

mysql> select nullif(2,5);
+-------------+
| nullif(2,5) |
+-------------+
|           2 |
+-------------+
1 row in set (0.00 sec)

mysql> 

mysql> select least(5,2,3,4);#Least()代表返回最小的参数
+----------------+
| least(5,2,3,4) |
+----------------+
|              2 |
+----------------+
1 row in set (0.00 sec)

mysql> select least(stuid,couid,scmark) from tb_score where scid=10;
+---------------------------+
| least(stuid,couid,scmark) |
+---------------------------+
|                      82.5 |
+---------------------------+
1 row in set (0.00 sec)

mysql> select stuid,couid,scmark from tb_score where scid=10;
+-------+-------+--------+
| stuid | couid | scmark |
+-------+-------+--------+
|  1033 |  5555 |   82.5 |
+-------+-------+--------+
1 row in set (0.00 sec)

mysql>


mysql> select t.* from tb_score t where t.scmark not between 95.0 and 78.0; #Not between A and B代表检查值是否不在A和B的范围之内  区间不要写反了
+------+-------+-------+---------------------+--------+
| scid | stuid | couid | scdate              | scmark |
+------+-------+-------+---------------------+--------+
|    1 |  1001 |  1111 | 2017-09-01 00:00:00 |   95.0 |
|    2 |  1001 |  2222 | 2017-09-01 00:00:00 |   87.5 |
|    3 |  1001 |  3333 | 2017-09-01 00:00:00 |  100.0 |
|    5 |  1001 |  6666 | 2017-09-02 00:00:00 |  100.0 |
|    6 |  1002 |  1111 | 2017-09-03 00:00:00 |   65.0 |
|    7 |  1002 |  5555 | 2017-09-01 00:00:00 |   42.0 |
|    8 |  1033 |  1111 | 2017-09-03 00:00:00 |   92.5 |
|    9 |  1033 |  4444 | 2017-09-01 00:00:00 |   78.0 |
|   10 |  1033 |  5555 | 2017-09-01 00:00:00 |   82.5 |
|   11 |  1572 |  1111 | 2017-09-02 00:00:00 |   78.0 |
|   12 |  1378 |  1111 | 2017-09-05 00:00:00 |   82.0 |
|   13 |  1378 |  7777 | 2017-09-02 00:00:00 |   65.5 |
|   14 |  2035 |  7777 | 2018-09-03 00:00:00 |   88.0 |
|   18 |  3755 |  9999 | 2017-09-01 00:00:00 |   92.0 |
+------+-------+-------+---------------------+--------+
14 rows in set (0.00 sec)

mysql> select t.* from tb_score t where t.scmark not between 78.0 and 95.0;
+------+-------+-------+---------------------+--------+
| scid | stuid | couid | scdate              | scmark |
+------+-------+-------+---------------------+--------+
|    3 |  1001 |  3333 | 2017-09-01 00:00:00 |  100.0 |
|    5 |  1001 |  6666 | 2017-09-02 00:00:00 |  100.0 |
|    6 |  1002 |  1111 | 2017-09-03 00:00:00 |   65.0 |
|    7 |  1002 |  5555 | 2017-09-01 00:00:00 |   42.0 |
|   13 |  1378 |  7777 | 2017-09-02 00:00:00 |   65.5 |
+------+-------+-------+---------------------+--------+
5 rows in set (0.00 sec)

mysql> select t.* from tb_score t ;
+------+-------+-------+---------------------+--------+
| scid | stuid | couid | scdate              | scmark |
+------+-------+-------+---------------------+--------+
|    1 |  1001 |  1111 | 2017-09-01 00:00:00 |   95.0 |
|    2 |  1001 |  2222 | 2017-09-01 00:00:00 |   87.5 |
|    3 |  1001 |  3333 | 2017-09-01 00:00:00 |  100.0 |
|    4 |  1001 |  4444 | 2018-09-03 00:00:00 |   NULL |
|    5 |  1001 |  6666 | 2017-09-02 00:00:00 |  100.0 |
|    6 |  1002 |  1111 | 2017-09-03 00:00:00 |   65.0 |
|    7 |  1002 |  5555 | 2017-09-01 00:00:00 |   42.0 |
|    8 |  1033 |  1111 | 2017-09-03 00:00:00 |   92.5 |
|    9 |  1033 |  4444 | 2017-09-01 00:00:00 |   78.0 |
|   10 |  1033 |  5555 | 2017-09-01 00:00:00 |   82.5 |
|   11 |  1572 |  1111 | 2017-09-02 00:00:00 |   78.0 |
|   12 |  1378 |  1111 | 2017-09-05 00:00:00 |   82.0 |
|   13 |  1378 |  7777 | 2017-09-02 00:00:00 |   65.5 |
|   14 |  2035 |  7777 | 2018-09-03 00:00:00 |   88.0 |
|   15 |  2035 |  9999 | 2020-08-01 00:00:00 |   NULL |
|   16 |  3755 |  1111 | 2020-08-01 00:00:00 |   NULL |
|   17 |  3755 |  8888 | 2020-08-01 00:00:00 |   NULL |
|   18 |  3755 |  9999 | 2017-09-01 00:00:00 |   92.0 |
+------+-------+-------+---------------------+--------+
18 rows in set (0.00 sec)

mysql>
mysql> select * from tb_student where stuaddr like '四川%';#Like代表字符匹配
+-------+-----------+--------+------------+--------------+--------+
| stuid | stuname   | stusex | stubirth   | stuaddr      | collid |
+-------+-----------+--------+------------+--------------+--------+
|  1001 | 杨逍      |       | 1990-03-04 | 四川成都     |      1 |
|  1033 | 王语嫣    |        | 1989-12-03 | 四川成都     |      1 |
|  1378 | 纪嫣然    |        | 1995-08-12 | 四川绵阳     |      1 |
|  3923 | 杨不悔    |        | 1985-04-17 | 四川成都     |      3 |
+-------+-----------+--------+------------+--------------+--------+
4 rows in set (0.00 sec)

mysql>

mysql> select * from tb_student where stuaddr <> '四川成都';
+-------+-----------+--------+------------+--------------+--------+
| stuid | stuname   | stusex | stubirth   | stuaddr      | collid |
+-------+-----------+--------+------------+--------------+--------+
|  1002 | 任我行    |       | 1992-02-02 | 湖南长沙     |      1 |
|  1378 | 纪嫣然    |        | 1995-08-12 | 四川绵阳     |      1 |
|  1572 | 岳不群    |       | 1993-07-19 | 陕西咸阳     |      1 |
|  1954 | 林平之    |       | 1994-09-20 | 福建莆田     |      1 |
|  3011 | 林震南    |       | 1985-12-12 | 福建莆田     |      3 |
+-------+-----------+--------+------------+--------------+--------+
5 rows in set (0.00 sec)

mysql> select * from tb_student where stuaddr != '四川成都';
+-------+-----------+--------+------------+--------------+--------+
| stuid | stuname   | stusex | stubirth   | stuaddr      | collid |
+-------+-----------+--------+------------+--------------+--------+
|  1002 | 任我行    |       | 1992-02-02 | 湖南长沙     |      1 |
|  1378 | 纪嫣然    |        | 1995-08-12 | 四川绵阳     |      1 |
|  1572 | 岳不群    |       | 1993-07-19 | 陕西咸阳     |      1 |
|  1954 | 林平之    |       | 1994-09-20 | 福建莆田     |      1 |
|  3011 | 林震南    |       | 1985-12-12 | 福建莆田     |      3 |
+-------+-----------+--------+------------+--------------+--------+
5 rows in set (0.00 sec)

• =号对比操作符

• mysql> SELECT 1 = 0;

• -> 0

• mysql> SELECT '0' = 0;

• -> 1

• mysql> SELECT '0.0' = 0;

• -> 1

• mysql> SELECT '0.01' = 0;

• -> 0

• mysql> SELECT '.01' = 0.01;

• -> 1

• <>/!=号对比操作符

• mysql> SELECT '.01' <> '0.01';

• -> 1

• mysql> SELECT .01 <> '0.01';

• -> 0

• mysql> SELECT 'zapp' <> 'zappp';

• -> 1

• <=小于等于对比操作符

• mysql> SELECT 0.1 <= 2;

• -> 1

• <小于对比操作符

• mysql> SELECT 2 < 2;

• -> 0

• >=大于等于对比操作符

• mysql> SELECT 2 >= 2;

• -> 1

• >大于对比操作符

• mysql> SELECT 2 > 2;

• -> 0

• is操作符

• mysql> SELECT 1 IS TRUE, 0 IS FALSE, NULL IS UNKNOWN;

• -> 1, 1, 1

• Is not操作符

• mysql> SELECT 1 IS NOT UNKNOWN, 0 IS NOT UNKNOWN, NULL IS

NOT UNKNOWN;

• -> 1, 1, 0

• Is null对比操作符

• mysql> SELECT 1 IS NULL, 0 IS NULL, NULL IS NULL;

• -> 0, 0, 1

• Is not null对比操作符

• mysql> SELECT 1 IS NOT NULL, 0 IS NOT NULL, NULL IS NOT NULL;

• -> 1, 1, 0

• Expr between min and max对比操作符

• 相当于min <= expr AND expr <= max

• mysql> SELECT 2 BETWEEN 1 AND 3, 2 BETWEEN 3 and 1;

• -> 1, 0

• mysql> SELECT 1 BETWEEN 2 AND 3;

• -> 0

• mysql> SELECT 'b' BETWEEN 'a' AND 'c';

• -> 1

• mysql> SELECT 2 BETWEEN 2 AND '3';

• -> 1

• mysql> SELECT 2 BETWEEN 2 AND 'x-3';

• -> 0

• expr IN (value,...)对比操作符

• 当expr值能在values中找到，则返回1，否则返回0

• mysql> SELECT 2 IN (0,3,5,7);

• -> 0

• mysql> SELECT 'wefwf' IN ('wee','wefwf','weg');

• -> 1

• mysql> SELECT (3,4) IN ((1,2), (3,4));

• -> 1

• mysql> SELECT (3,4) IN ((1,2), (3,5));

• -> 0

• expr NOT IN (value,...)对比操作符

• Isnull(expr)操作符

• 如果expr是null，则返回1，否则返回0

• mysql> SELECT ISNULL(1+1);

• -> 0

• mysql> SELECT ISNULL(1/0);

• -> 1

• LEAST(value1,value2,...)

• 返回最小值，如果其中有值为null，则返回null

• mysql> SELECT LEAST(2,0);

• -> 0

• mysql> SELECT LEAST(34.0,3.0,5.0,767.0);

• -> 3.0

• mysql> SELECT LEAST('B','A','C');

• -> 'A'

逻辑操作符

• 逻辑操作符返回1 (TRUE), 0 (FALSE), 或者NULL

• NOT, !逻辑操作符代表非操作

• And,&&逻辑操作符

mysql> select not 10,! 10,not 0;
+--------+------+-------+
| not 10 | ! 10 | not 0 |
+--------+------+-------+
|      0 |    0 |     1 |
+--------+------+-------+
1 row in set (0.00 sec)

mysql> select 1 and 0,1 and 1,null and 0,null and 1;
+---------+---------+------------+------------+
| 1 and 0 | 1 and 1 | null and 0 | null and 1 |
+---------+---------+------------+------------+
|       0 |       1 |          0 |       NULL |
+---------+---------+------------+------------+
1 row in set (0.00 sec)

mysql>

• Or, ||逻辑操作符

mysql> select  1 or 0,1 or 1,0 or 0,0 or null,1 or null;
+--------+--------+--------+-----------+-----------+
| 1 or 0 | 1 or 1 | 0 or 0 | 0 or null | 1 or null |
+--------+--------+--------+-----------+-----------+
|      1 |      1 |      0 |      NULL |         1 |
+--------+--------+--------+-----------+-----------+
1 row in set (0.00 sec)

mysql>

• Xor逻辑操作符 “XOR”表示逻辑异或,当任意一个操作数为NULL时,返回值为NULL，对于非NULL的操作数,如果两个的逻辑真假值相异，则返回结果为1，否则为0,就是两个不能同时成立,也不能同时不成立,只成立其中一个条件

mysql> select 1 xor 0,1 xor 1,0 xor 0,null xor 0;
+---------+---------+---------+------------+
| 1 xor 0 | 1 xor 1 | 0 xor 0 | null xor 0 |
+---------+---------+---------+------------+
|       1 |       0 |       0 |       NULL |
+---------+---------+---------+------------+
1 row in set (0.00 sec)

mysql>

• 分配操作符是指赋值操作

• mysql> SELECT @var1, @var2;

• -> NULL, NULL

• mysql> SELECT @var1 := 1, @var2;

• -> 1, NULL

• mysql> SELECT @var1, @var2;

• -> 1, NULL

• mysql> SELECT @var1, @var2 := @var1;

• -> 1, 1

• mysql> SELECT @var1, @var2;

• -> 1, 1

• mysql> SELECT @var1:=COUNT(*) FROM t1;

• -> 4

• mysql> SELECT @var1;

• -> 4

mysql> select @a1,@a2;
+------+------+
| @a1  | @a2  |
+------+------+
| NULL | NULL |
+------+------+
1 row in set (0.00 sec)

mysql> select @a1:='ABCabc',@a2;
+---------------+------+
| @a1:='ABCabc' | @a2  |
+---------------+------+
| ABCabc        | NULL |
+---------------+------+
1 row in set, 1 warning (0.00 sec)

mysql> select @a1,@a2;
+--------+------+
| @a1    | @a2  |
+--------+------+
| ABCabc | NULL |
+--------+------+
1 row in set (0.00 sec)

mysql> set @a2='DEF';
Query OK, 0 rows affected (0.00 sec)

mysql> select @a1,@a2;
+--------+------+
| @a1    | @a2  |
+--------+------+
| ABCabc | DEF  |
+--------+------+
1 row in set (0.00 sec)

mysql

• :=操作符也可以用在update等语句

• mysql> SELECT @var1;

• -> 4

• mysql> SELECT * FROM t1;

• -> 1, 3, 5, 7

• mysql> UPDATE t1 SET c1 = 2 WHERE c1 = @var1:= 1;

• Query OK, 1 row affected (0.00 sec)

• Rows matched: 1 Changed: 1 Warnings: 0

• mysql> SELECT @var1;

• -> 1

• mysql> SELECT * FROM t1;

• -> 2, 3, 5, 7

mysql> select @a1;
+--------+
| @a1    |
+--------+
| ABCabc |
+--------+
1 row in set (0.00 sec)

mysql> select * from tb_student;
+-------+--------------+--------+------------+--------------+--------+
| stuid | stuname      | stusex | stubirth   | stuaddr      | collid |
+-------+--------------+--------+------------+--------------+--------+
|  1001 | 杨逍         |       | 1990-03-04 | 四川成都     |      1 |
|  1002 | 任我行       |       | 1992-02-02 | 湖南长沙     |      1 |
|  1033 | 王语嫣       |        | 1989-12-03 | 四川成都     |      1 |
|  1378 | 纪嫣然       |        | 1995-08-12 | 四川绵阳     |      1 |
|  1572 | 岳不群       |       | 1993-07-19 | 陕西咸阳     |      1 |
|  1954 | 林平之       |       | 1994-09-20 | 福建莆田     |      1 |
|  2035 | 东方不败     |       | 1988-06-30 | NULL         |      2 |
|  3011 | 林震南       |       | 1985-12-12 | 福建莆田     |      3 |
|  3755 | 项少龙       |       | 1993-01-25 | NULL         |      3 |
|  3923 | 杨不悔       |        | 1985-04-17 | 四川成都     |      3 |
+-------+--------------+--------+------------+--------------+--------+
10 rows in set (0.00 sec)

mysql> update tb_student  set stuaddr=@a1 where stuid=1001;
Query OK, 1 row affected (0.07 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> select * from tb_student where stuid=1001;
+-------+---------+--------+------------+---------+--------+
| stuid | stuname | stusex | stubirth   | stuaddr | collid |
+-------+---------+--------+------------+---------+--------+
|  1001 | 杨逍    |       | 1990-03-04 | ABCabc  |      1 |
+-------+---------+--------+------------+---------+--------+
1 row in set (0.00 sec)

mysql>

• =操作符在两种情况下会被认为是赋值操作，而其他情况下会认

为是对比操作符

• 在set语句中，=操作符会被认为是赋值操作

• mysql> set @a=1;

• mysql> select @a;

• +------+

• | @a |

• +------+

• | 1 |

• 在update语句中的set子句中，=操作符会被认为是赋值操作

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原文地址：https://www.cnblogs.com/laonicc/p/13394463.html