P_olaris7的博客

do-while ,while,for

Group by 不能用select * 语句 Having 放在group by的后面. Select xx ,xx from 表名 where group by xx.xx having order by 表名 desc/asc; Count(*) count() SELECT * FROM studentinfo GROUP BY city HAVING AVG(age)>20 LIMIT 1;

-- >查询出学生表中年龄为22或者24的学生信息 ,不要小括号,加小括号会报错. -- SELECT * FROM studentinfo WHERE age = (22 or 24); -- 这个也是错的 -- SELECT * FROM studentinfo WHERE age = 22 or 24; SELECT * FROM studentinfo where age in 22 or age IN 24; -- >查询出学生表中地址不为上海和深圳的所有学生信息. SELECT *

SELECT * FROM studentinfo WHERE city <>'上海'; -- >!和=之间切勿用空格 SELECT * FROM studentinfo WHERE city != '上海';