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修改mysql配置文件，然后添加 skip-name-resolve，跳过解析[mysqld]skip-name-resolve

SELECT d.index as days,d.date as time,COUNT(a.id) as count_numFROM(SELECT @a :=@a + 1 as `index`, DATE(ADDDATE(CURRENT_DATE, INTERVAL @a DAY)) AS `date`FROM mysql.help_topic,(SELECT @a := 0) tempWHERE @a < 6 - WEEKDAY(CURRENT_DATE)UNIONSELECT @s :

下载地址不要安装错了，不然初始化数据库的时候会报错解压tar -xvf 文件名移动并重命名一下mv mysql-5.7.26-linux-glibc2.12-x86_64 /usr/local/mysql配置my.cnfvim /etc/my.cnf[mysqld]bind-address=0.0.0.0port=3306user=rootbasedir=/usr/local/mysqldatadir=/data/mysqlsocket=/tmp/mysql.sockl

去重# 查询员工表涉及到的部门编号SELECT DISTINCT department_id FROM employees示例：concat 连接字段逻辑运算符orin判断某字段的值是否属于in列表中的某一项#查询员工表jobid等于AD_VP，AD_PRES的员工姓名SELECT last_name,job_id FROM employees WHERE job_id='AD_VP' OR job_id='AD_PRES' #使用in 等价于orSELECT last_