我做一个统计页面效果是
所建立的数据库表是
求解怎么用php实现，谢谢！
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回复讨论(解决方案)
一条 SQL 指令就可完成
@xuzuning
大神。。。。。。一条怕是不行吧！
确实一条可以，按部就班一个个项加进去
我是菜鸟啊！完全使不上劲！
select 班级, count(*) as 人数, sum(分数) as 总分数, sum(if(成绩是否有效='是',1,0) as 有效人数, sum(if(成绩是否有效='是',分数,0) as 有效成绩 ........
不写了，你偷懒用截图，我也不想打字
@xuzuning sum(if(成绩是否有效='是',1,0))这个算不出成绩有效人数啊
用group by 和having试试
@xuzuning @jmy454157571
sql是对了，可是Php循环输出不了
$mysqli=new mysqli("localhost","root","","car_insure");
$mysqli->set_charset("utf8");
if($mysqli->connect_error){
die("连接失败".$mysqli->conect_error);
}
$sql="select t3.*,t4.totalNum as '无效总人数',t4.totalScore as '无效总分数' from
(select t1.class_ as '班级',t1.totalNum as '总人数',t1.totalScore as '总得分',t2.totalNum as '有效总人数',t2.totalScore as '有效总得分' from (select class_,count(id_) as totalNum,sum(score_) as totalScore from score group by class_) as t1 left join (select class_,count(id_) as totalNum,sum(score_) as totalScore from score group by class_,flag_ having flag_='是') as t2 on t1.class_=t2.class_)
as t3
left join (select class_,count(id_) as totalNum,sum(score_) as totalScore from score group by class_,flag_ having flag_='否') as t4
on t3.`班级`=t4.class_"
$res=$mysqli->query($sql);
if($res){
echo"2222";
}else{
echo"1111";
}
$mysqli->close();
?>
输出是1111
这是怎么回事儿，$res没取到值啊！麻烦看下哪里的问题
sql语句在Mysql里面查询出来是对的。
