LIMIT

用于指定要返回的记录数量

示例：

select *
from employees limit 3;

+--------+------------+------------+-----------+--------+------------+
| emp_no | birth_date | first_name | last_name | gender | hire_date  |
+--------+------------+------------+-----------+--------+------------+
|  10001 | 1953-09-02 | Georgi     | Facello   | M      | 1986-06-26 |
|  10002 | 1964-06-02 | Bezalel    | Simmel    | F      | 1985-11-21 |
|  10003 | 1959-12-03 | Parto      | Bamford   | M      | 1986-08-28 |
+--------+------------+------------+-----------+--------+------------+
3 rows in set (0.00 sec)

LIKE

使用LIKE运算符来搜索列中的指定模式

• ％(百分号表示零个，一个或多个字符)
• _(下划线表示单个字符)

示例：

select *
from employees
where last_name like '%ce_l_'AND first_name like 'G_o%g_';

+--------+------------+------------+-----------+--------+------------+
| emp_no | birth_date | first_name | last_name | gender | hire_date  |
+--------+------------+------------+-----------+--------+------------+
|  10001 | 1953-09-02 | Georgi     | Facello   | M      | 1986-06-26 |
|  55649 | 1956-01-23 | Georgi     | Facello   | M      | 1988-05-04 |
+--------+------------+------------+-----------+--------+------------+
2 rows in set (0.10 sec)

AS

别名

示例：

select emp.first_name as name
from employees as emp limit 3;

+---------+
| name    |
+---------+
| Georgi  |
| Bezalel |
| Parto   |
+---------+
3 rows in set (0.01 sec)

CREATE UNIQUE INDEX、DROP INDEX

创建唯一索引

示例：

-- 设置id为唯一索引，名称为id_name
create unique index id_name on order_table (id);-- 删除唯一索引
drop index id_name on order_table;

CREATE VIEW、DROP VIEW

创建新视图

视图（View）是一种虚拟存在的表，视图也由列和行构成，但视图并不实际存在于数据库中。行和列的数据来自于定义视图的查询中所使用的表，并且还是在使用视图时动态生成的。视图中的数据是依赖于真实表中的数据的。一旦真实表中的数据发生改变，显示在视图中的数据也会发生改变

示例：

-- 创建视图
create view order_view as
select date_01
from order_table
where id = 3;
-- 删除视图
drop view order_view;
-- 查询视图数据
select *
from order_view;

+------------+
| date_01    |
+------------+
| 2023-07-03 |
+------------+
1 row in set (0.00 sec)

GROUP BY

通过…分组

示例：

-- 通过员工编号分组查询员工编号、薪资数、薪资和、薪资平均值、薪资最大值、薪资最小值
select emp_no, count(salary), sum(salary), avg(salary), max(salary), min(salary)
from salaries
group by emp_no;

+--------+---------------+-------------+-------------+-------------+-------------+
| emp_no | count(salary) | sum(salary) | avg(salary) | max(salary) | min(salary) |
+--------+---------------+-------------+-------------+-------------+-------------+
|  10001 |            17 |     1281612 |  75388.9412 |       88958 |       60117 |
|  10002 |             6 |      413127 |  68854.5000 |       72527 |       65828 |
|  10003 |             7 |      301212 |  43030.2857 |       43699 |       40006 |
|  10004 |            16 |      904196 |  56512.2500 |       74057 |       40054 |
|  10005 |            13 |     1134585 |  87275.7692 |       94692 |       78228 |
+--------+---------------+-------------+-------------+-------------+-------------+
5 rows in set (0.00 sec)

HAVING

筛选分组后的各组数据

示例：

-- 按员工编号分组查询薪资总和大于2300000的数据
select emp_no, sum(salary)
from salaries
group by emp_no
having sum(salary) > 2300000;

+--------+-------------+
| emp_no | sum(salary) |
+--------+-------------+
|  43624 |     2492873 |
|  47978 |     2374024 |
|  66793 |     2383923 |
|  68086 |     2305351 |
|  80823 |     2368170 |
| 109334 |     2553036 |
| 237542 |     2381119 |
+--------+-------------+
7 rows in set (0.77 sec)

MYSQL - JOIN

示例表（table_01、table_02）：

select *
from table_01;
select *
from table_02;

+----+
| id |
+----+
|  1 |
|  2 |
|  3 |
|  4 |
|  5 |
|  6 |
+----+
6 rows in set (0.00 sec)+----+
| id |
+----+
|  4 |
|  5 |
|  6 |
|  7 |
|  8 |
|  9 |
|  0 |
+----+
7 rows in set (0.00 sec)

INNER JOIN、JOIN

可以简写为JOIN

示例：

select *
from table_01join table_02 on table_01.id = table_02.id;
select *
from table_01inner join table_02 on table_01.id = table_02.id;

+----+----+
| id | id |
+----+----+
|  4 |  4 |
|  5 |  5 |
|  6 |  6 |
+----+----+
3 rows in set (0.00 sec)

示例：

-- 查询管理员所在部门和姓名等信息
select employees.emp_no,employees.first_name,employees.last_name,employees.gender,departments.dept_no,departments.dept_name
from dept_managerjoin departments on dept_manager.dept_no = departments.dept_nojoin employees on employees.emp_no = dept_manager.emp_no;

+--------+-------------+--------------+--------+---------+-----------+
| emp_no | first_name  | last_name    | gender | dept_no | dept_name |
+--------+-------------+--------------+--------+---------+-----------+
| 111692 | Tonny       | Butterworth  | F      | d009    | ????      |
| 111784 | Marjo       | Giarratana   | F      | d009    | ????      |
| 111877 | Xiaobin     | Spinelli     | F      | d009    | ????      |
| 111939 | Yuchang     | Weedman      | M      | d009    | ????      |
| 110511 | DeForest    | Hagimont     | M      | d005    | ????      |
| 110567 | Leon        | DasSarma     | F      | d005    | ????      |
| 110183 | Shirish     | Ossenbruggen | F      | d003    | ??        |
| 110228 | Karsten     | Sigstam      | F      | d003    | ??        |
| 110303 | Krassimir   | Wegerle      | F      | d004    | ??        |
| 110344 | Rosine      | Cools        | F      | d004    | ??        |
| 110386 | Shem        | Kieras       | M      | d004    | ??        |
| 110420 | Oscar       | Ghazalie     | M      | d004    | ??        |
| 111035 | Przemyslawa | Kaelbling    | M      | d007    | ??        |
| 111133 | Hauke       | Zhang        | M      | d007    | ??        |
| 110725 | Peternela   | Onuegbe      | F      | d006    | ??        |
| 110765 | Rutger      | Hofmeyr      | F      | d006    | ??        |
| 110800 | Sanjoy      | Quadeer      | F      | d006    | ??        |
| 110854 | Dung        | Pesch        | M      | d006    | ??        |
| 110085 | Ebru        | Alpin        | M      | d002    | ??        |
| 110114 | Isamu       | Legleitner   | F      | d002    | ??        |
| 111400 | Arie        | Staelin      | M      | d008    | ????      |
| 111534 | Hilary      | Kambil       | F      | d008    | ????      |
| 110022 | Margareta   | Markovitch   | M      | d001    | ??        |
| 110039 | Vishwani    | Minakawa     | M      | d001    | ??        |
+--------+-------------+--------------+--------+---------+-----------+
24 rows in set (0.00 sec)

LEFT JOIN、LEFT OUTER JOIN

示例：

select *
from table_01left join table_02 on table_01.id = table_02.id;

+----+------+
| id | id   |
+----+------+
|  1 | NULL |
|  2 | NULL |
|  3 | NULL |
|  4 |    4 |
|  5 |    5 |
|  6 |    6 |
+----+------+
6 rows in set (0.00 sec)

RIGHT JOIN、RIGHT OUTER JOIN

示例：

select *
from table_01right join table_02 on table_01.id = table_02.id;

+------+----+
| id   | id |
+------+----+
|    4 |  4 |
|    5 |  5 |
|    6 |  6 |
| NULL |  7 |
| NULL |  8 |
| NULL |  9 |
| NULL |  0 |
+------+----+
7 rows in set (0.00 sec)

LEFT JOIN ... WHERE ...

示例：

select *
from table_01left join table_02 on table_01.id = table_02.id
where table_02.id is null;

+----+------+
| id | id   |
+----+------+
|  1 | NULL |
|  2 | NULL |
|  3 | NULL |
+----+------+
3 rows in set (0.00 sec)

RIIGHT JOIN ... WHERE ...

示例：

select *
from table_01right join table_02 on table_01.id = table_02.id
where table_01.id is null;

+------+----+
| id   | id |
+------+----+
| NULL |  7 |
| NULL |  8 |
| NULL |  9 |
| NULL |  0 |
+------+----+
4 rows in set (0.00 sec)

TRUNCATE TABLE

删除表中的所有数据

示例：

truncate table table_name;

INSERT INTO 表1 (列1, 列2) SELECT (列1, 列2) FROM 表2

把表2数据复制到表1中

示例：

insert into table_02 (id) (select * from table_01);

+----+
| id |
+----+
|  4 |
|  5 |
|  6 |
|  7 |
|  8 |
|  9 |
|  0 |
|  1 |
|  2 |
|  3 |
|  4 |
|  5 |
|  6 |
+----+
13 rows in set (0.00 sec)

UNION、UNION ALL

组合两个或更多SELECT语句的结果集

UNION 不返回任何重复的行

UNION ALL 返回重复的行

要求：

• UNION中的每个SELECT语句必须具有相同的列数
• 这些列也必须具有相似的数据类型
• 每个SELECT语句中的列也必须以相同的顺序排列
• 每个SELECT语句必须有相同数目的列表达式
• 但是每个SELECT语句的长度不必相同

示例(UNION)：

select dept_no
from dept_manager
union
select dept_no
from departments;

+---------+
| dept_no |
+---------+
| d001    |
| d002    |
| d003    |
| d004    |
| d005    |
| d006    |
| d007    |
| d008    |
| d009    |
+---------+
9 rows in set (0.00 sec)

示例(UNION ALL)：

select dept_no
from dept_manager
union all
select dept_no
from departments;

+---------+
| dept_no |
+---------+
| d001    |
| d001    |
| d002    |
| d002    |
| d003    |
| d003    |
| d004    |
| d004    |
| d004    |
| d004    |
| d005    |
| d005    |
| d006    |
| d006    |
| d006    |
| d006    |
| d007    |
| d007    |
| d008    |
| d008    |
| d009    |
| d009    |
| d009    |
| d009    |
| d009    |
| d005    |
| d003    |
| d004    |
| d007    |
| d006    |
| d002    |
| d008    |
| d001    |
+---------+
33 rows in set (0.00 sec)

日期相关函数

NOW()、CURDATE()、CURTIME()、DATE()、DATE_FORMAT()、DATEDIFF()

示例：

-- NOW()	                                    返回当前的日期和时间
-- CURDATE()	                                返回当前的日期
-- CURTIME()	                                返回当前的时间
-- DATE('2023-07-12 08:00:09')                  提取日期或日期/时间表达式的日期部分
-- DATE_FORMAT(NOW(),'%b %d %Y %h:%i %p')       用不同的格式显示日期/时间
-- DATEDIFF('2023-07-12 08:00:09','2008-11-29') 返回两个日期之间的天数
select NOW(),CURDATE(),CURTIME(), DATE ('2023-07-12 08:00:09'), DATE_FORMAT(NOW(), '%b %d %Y %h:%i %p'), DATEDIFF('2023-07-12 08:00:09', '2008-11-29');

+---------------------+------------+-----------+-----------------------------+-----------------------------------------+-----------------------------------------------+
| NOW()               | CURDATE()  | CURTIME() | DATE('2023-07-12 08:00:09') | DATE_FORMAT(NOW(), '%b %d %Y %h:%i %p') | DATEDIFF('2023-07-12 08:00:09', '2008-11-29') |
+---------------------+------------+-----------+-----------------------------+-----------------------------------------+-----------------------------------------------+
| 2023-07-12 08:06:49 | 2023-07-12 | 08:06:49  | 2023-07-12                  | Jul 12 2023 08:06 AM                    |                                          5338 |
+---------------------+------------+-----------+-----------------------------+-----------------------------------------+-----------------------------------------------+
1 row in set (0.00 sec)

EXTRACT()、DATE_ADD()、DATE_SUB()

示例：

-- EXTRACT()    返回日期/时间的单独部分
-- DATE_ADD()	向日期添加指定的时间间隔
-- DATE_SUB()	从日期减去指定的时间间隔
select EXTRACT(YEAR from NOW()), DATE_ADD(NOW(), interval 5 day), DATE_SUB(NOW(), interval 15 day);

+--------------------------+---------------------------------+----------------------------------+
| EXTRACT(YEAR from NOW()) | DATE_ADD(NOW(), interval 5 day) | DATE_SUB(NOW(), interval 15 day) |
+--------------------------+---------------------------------+----------------------------------+
|                     2023 | 2023-07-17 08:11:06             | 2023-06-27 08:11:06              |
+--------------------------+---------------------------------+----------------------------------+
1 row in set (0.00 sec)