数据库|mysql教程
数据库,统计,如何
数据库-mysql教程
首先准备四张表A、B、C、D，
——————————–A|B |C |Da b | a c | a d | d e1 1 | 1 1 | 1 A | A 12 2 | 1 3 | 2 B | B 23 4 | 1 4 | 3 C | C 34 6 | 2 1 | 4 D | D 4——————————–
下面我们需要用一条sql语句将A表所有的列，B表对与A表a字段相关联的列求count,通过C表,将D表与A表关联起来，得到的结果如下：
1 1 3 12 2 1 23 4 0 34 6 0 4
php网站统计源码,自己的域名ubuntu,tomcat更换图片没变,爬虫csv文档,达内培训php费用,seo主要是学什么seo教程lzw
Mysql语句解决：
select A.a,A.b,IFNULL(c,0) as c,D.a from (select 1 as a,2 as b union allselect 2 as a,2 as b union allselect 3 as a,4 as b union allselect 4 as a,6 as b) as A left outer join(select a,count(a) as c from(select 1 as a,3 as c union allselect 1 as a,3 as c union allselect 1 as a,3 as c union allselect 2 as a,3 as c ) B group by a) as Bon A.a=B.a join (select 1 as a,’A’ as d union allselect 2 as a,’B’ as d union allselect 3 as a,’C’ as d union allselect 4 as a,’D’ as d ) as C on A.a=C.a join(select 1 as a,’A’ as d union allselect 2 as a,’B’ as d union allselect 3 as a,’C’ as d union allselect 4 as a,’D’ as d ) as Don D.d=C.d
html访问网页源码,vscode默认是什么字体,ubuntu 移除文件,tomcat默认监听端口,博主爬虫,php去除空格 换行,荆门广告seo推广哪个好,网站声明js代码,早讯网模板dedecmslzw
