查詢學生的總分
select name, math + English + China as '總分' from students;
在姓趙的學生總分基礎上， 增加60%，
select name, round((math + English + China) * 1.6, 2) as '新的總分' where name like '趙%';
注意round函數的使用， 能夠使結果保留兩位小數
where語句
查詢英語成績大于90的學生的成績
select * from students where English > 90;
查詢總分大于200的學生的成績
select id, name, (math + English + China) as '總分' from students where (math + English + China) > 200;
查詢姓名為趙，但是id<90的學生
select * from students where name like '趙%' and id < 90;
查詢英語成績大于語文成績的學生
select * from students where English > China;
查詢總分大于200，并且數學成績小于語文成績的姓宋的學生
select * from students where (math + English + China) > 200 and math > China and name like '宋%';
查詢英語成績在80-90 之間的學生
select * from students where English between 80 and 90;
等價于
select * from students where English >=80 and English <= 90;
查詢數學成績為89， 90， 91的學生
select * from students where math = 90 or math = 89 or math =91;
select * from students where math in (89, 90, 91); (推薦)
order by語句
舉例：
按照數學成績 升序排序
select * from students order by math;
按照數學成績 降序排序
select * from students order by math desc;
按照學生總分降序排列 注意order by 后面 跟的字段 或者是別名， 不能帶 '';
select id, name, (English + math + China) as 'totalscore' from students order by totalscore;
對姓李的學生總成績進行排序
select id, name, (English + math + China) as 'totalscore' from students where name like '李%' order by totalscore；
