SQL基础

• 现在有一个学生表，一个课程成绩表，请问，怎么找出学生课程的最高分数，谈一谈思路

• 现在，有一个组合索引（A,B,C），可以有哪几种查询方式？

考察点：sql语句
参考回答：

优: select * from test where a=10 and b>50

差: select * from test where b = 50

优: select * from test order by a

差: select * from test order by b

差: select * from test order by c

优: select * from test where a=10 order by a

优: select * from test where a=10 order by b

差: select * from test where a=10 order by c

优: select * from test where a>10 order by a

差: select * from test where a>10 order by b

差: select * from test where a>10 order by c

优: select * from test where a=10 and b=10 order by a

优: select * from test where a=10 and b=10 order by b

优: select * from test where a=10 and b=10 order by c

优: select * from test where a=10 and b=10 order by a

优: select * from test where a=10 and b>10 order by b

差: select * from test where a=10 and b>10 order by c

• 写SQL：找出每个城市的最新一条记录。

考察点：sql语句
参考回答：

id 城市 人口 信息 创建时间
1 北京 100 info1 时间戳
2 北京 100 info2 时间戳
3 上海 100 info3 时间戳
4 上海 100 info4 时间戳