MySQL语法-高级
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_01
join table_02 on table_01.id = table_02.id;
select *
from table_01
inner 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_manager
join departments on dept_manager.dept_no = departments.dept_no
join 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_01
left 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_01
right 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_01
left 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_01
right 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)