目录

一,union all 

二，GROUP_CONCAT函数

三，字符串函数：RIGHT()函数

四，字符串函数：LENGTH() 函数 /   REPLACE（）函数

五，条件更新表内的值

六，创建外键

七，修改表名

八，删除记录 

九，构建触发器

十，增加属性字段

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一,union all 

对查询结果进行连接 与 union 不同 union 不会去重

SELECT 
AVG(salary)
FROM `salaries8` 
WHERE to_date = '9999-01-01' AND salary NOT IN (SELECT MAX(salary) FROM `salaries8` AND to_date = '9999-01-01'UNION ALL SELECT MIN(salary) FROM `salaries8` AND to_date = '9999-01-01')

二，GROUP_CONCAT函数

 可以将分组后的相同字段连接

selectdept_no,group_concat(emp_no) employees
from dept_emp
group by dept_no;

三，字符串函数：RIGHT()函数

从右向左获取字段的值 可以指定获取的个数

SELECT
first_name
FROM `employees`
ORDER BY RIGHT(first_name,2)

四，字符串函数：LENGTH() 函数 /   REPLACE（）函数

LENGTH()函数用来获取字符串的长度 /  replace（字段，"被替换值"，”替换的值“）函数可以替换值

SELECT id, (LENGTH(string) - LENGTH(REPLACE(string,",",''))) AS cnt  FROM `strings`

update titles_test
set titles_test.emp_no = replace(titles_test.emp_no, 10001, 10005)
where titles_test.id = '5';

五，条件更新表内的值

UPDATE  ”table_name“ SET  `字段` = ”value“ WHERE 

-- 更新数据库
UPDATE `salaries6` SET salary = 1.1 * salary
WHERE salaries6.emp_no IN (SELECT emp_no FROM `emp_bonus`) AND salaries6.to_date = '9999-01-01'

update titles_test set to_date = NULL, from_date = "2001-01-01"
where id in
(
    select * from (
        select id
        from titles_test
        where to_date = "9999-01-01"
        ) as t
)

六，创建外键

ALTER TABLE audit ADD FOREIGN KEY (emp_no) REFERENCES employees_test(ID);

七，修改表名

ALTER TABLE `titles_test` RENAME AS `titles_2017`

八，删除记录 

delete from titles_test
where id not in(
select min_id from (select min(id) as min_id from titles_test group by emp_no)t1);

九，构建触发器

create trigger audit_log
after insert on employees_test
for each row
begininsert into audit values(new.id,new.name);
end

十，增加属性字段

ALTER TABLE actor ADD DELETE_date DATETIME NOT NULL DEFAULT '0000 00:00:00'