sql-3 关系数据库常用操作

SQL 常用操作

#数据抽出
select * from users order by score desc;
select * from users order by team,score desc;
select * from users order by score desc limit 3;  （offset偏移量，默认是0）
select * from users order by score desc limit 3 offset 2;

#数据统计（分组，求和，排序，复合）
1. distinct 过滤重复到数据
2. sum 求和函数
3. max/min 最大/最小值
4. group by/having 分组过滤

select distinct team from users;
select sum(score) from users;  (max,min)
select * from users where score = (select max(score) from users); 复合查询，取出表里得分最多球员的详细信息
select team, max(score) from users group by team having max(score) >= 25; having是针对 group by 的过滤条件，查询team max(score)，按照team分组，并且max(score)>=25
select team, max(score) from users group by team having max(score) >= 25 order by max(score),对结果进行排序

常用函数: