1.查询中用到的关键词主要包含六个:
select--from--where--group by--having--order by
2、执行顺序:
from--where--group by--having--select--order by
3、*where 后第一个条件尽量要过滤掉最多的信息
从哪里检索--检索条件(对条件过滤)--对过滤结果分组--对分组数据再次过滤--查看结果中的哪些列--按照什么顺序查看
-- 高到低的顺序显示个人平均分在70分以上的学生姓名和平均分,并去掉不及格的和名为‘mark’的信息
SELECT
s_name,
avg( score )
FROM
tbl_student
WHERE
score >= 60
AND s_name != 'mark'
GROUP BY
s_name
HAVING
avg( score ) >= 70
ORDER BY
avg( score ) DESC
顺序如下:
7 SELECT
8 DISTINCT <select_list>
1 FROM <left_table>
3 <join_type> JOIN <right_table>
2 ON <join_condition>
4 WHERE <where_condition>
5 GROUP BY <group_by_list>
6 HAVING <having_condition>
9 ORDER BY <order_by_condition>
10LIMIT <limit_number>