Sep 16, 2019 8:25:47 PM 共429人围观 0人评论

SELECT MAXemployees.salary,employees.job_id FROM employees GROUP BY employees.job_id;SELECT COUNT*,departments.location_id FROM departments GROUP BY location_id......

Sep 16, 2019 8:09:31 PM 共364人围观 0人评论

SELECT COUNTemployees.salary FROM employees; # 统计一列的个数 会忽略null值 SELECT COUNT* FROM employees; # 统计行数 不会忽略null SELECT COUNT1 FROM employees; # 统计行数 不会忽略null C......

Sep 16, 2019 6:01:37 PM 共356人围观 0人评论

SELECT SUMemployees.salary FROM employees;SELECT AVGemployees.salary FROM employees;SELECT MAXemployees.salary FROM employees;SELECT MINemployees.salary FROM em......

Sep 16, 2019 5:28:24 PM 共357人围观 0人评论

# IF类似于JAVA中的三目运算符 表达式1成立 则返回表达式2 反之 返回表达式3SELECT IF105,'大','小';SELECT employees.last_name,employees.commission_pct,IFemployees.commission_pct IS NULL,'呵呵没奖金','......

Sep 16, 2019 5:22:52 PM 共349人围观 0人评论

SELECT VERSION; # 版本SELECT DATABASE; # 当前数据库SELECT USER; # 当前用户