Псевдоним MYSQL в предложении where

Question

У меня есть запрос, и я хочу отфильтровать набор результатов, используя столбец ALIASED в моем состоянии WHERE, я прочитал, что вы не можете сделать это, но у меня пока нет альтернативного способа сделать это эффективно, так как я работаю над тысячами записей,

$str = "SELECT
                mainclass.id AS classid,
                mainclass.code AS classcode,
                Sum(CASE WHEN enroll.acctok = '1' AND enroll.assessed = '1'
                    THEN enroll.assessed 
                    ELSE 0 end) AS assessedinclass,
                Sum(enroll.validated = '1') AS validatedinclass,
                section.name AS sectionname,
                subject.code AS subcode,
                subject.subdesc,
                mainclass.units,
                sched.name AS schedule,
                mainclass.tutorial,
                mainclass.dissolved,
                mainclass.slots,
                mainclass.ismother,
                mergeclass.code AS mothercode,
                mergeclass.id AS mothercodeid,
                mergeclass.slots AS mothercodeslots,
                mainclass.mergein,
                mainclass.inst,
                instructor.lname,
                instructor.fname,
                instructor.mname,
                instructor.suffix
            FROM
                class AS mainclass
                Left Join enrolldet ON mainclass.id = enrolldet.class
                Left Join enroll ON enrolldet.enrollno = enroll.enrollno
                Inner Join period ON mainclass.period = period.id
                Inner Join section ON mainclass.section = section.id
                Inner Join subject ON mainclass.subject = subject.id
                Left Join sched ON mainclass.sched = sched.id
                Left Join class AS mergeclass ON mainclass.mergein = mergeclass.id
                Left Join instructor ON mainclass.inst = instructor.userid
                Left Join course ON section.course = course.id
             WHERE 
                (period.id = :period OR period.code = :period)";
    if($level != ''){
        $str .= " AND course.level = '".$level."'";
    }
    if($dept != ''){
        $str .= " AND course.dept = '".$dept."'";
    }
    if($display != ''){
        switch ($display) {
            case 'open':
                $str .= " AND mainclass.slots > assessedinclass";
                break;
            case 'dissolved':
                $str .= " AND mainclass.dissolved = 1";
                break;
            case 'tutorial':
                $str .= " AND mainclass.tutorial = 1";
                break;
            case 'closed':
                $str .= " AND mainclass.slots <= assessedinclass";
                break;
        }       
    }            
    $str .= "GROUP BY
                mainclass.id,
                mainclass.code";
    $str .= " ORDER BY subject.code, mainclass.id";
    return $this->_db->select($str,array(':period' => $period));   

я пытаюсь отфильтровать его, используя ASSESSEDINCLASS WHERE mainclass.slots> ASSESSEDINCLASS означает, что объект ОТКРЫТ

, а если mainclass.slots <= ASSESSEDINCLASS, он будет считаться ЗАКРЫТЫМ </p>

Answer 1

$str = "SELECT
            mainclass.id AS classid,
            mainclass.code AS classcode,
            Sum(CASE WHEN enroll.acctok = '1' AND enroll.assessed = '1'
                THEN enroll.assessed 
                ELSE 0 end) AS assessedinclass,
            Sum(enroll.validated = '1') AS validatedinclass,
            section.name AS sectionname,
            subject.code AS subcode,
            subject.subdesc,
            mainclass.units,
            sched.name AS schedule,
            mainclass.tutorial,
            mainclass.dissolved,
            mainclass.slots,
            mainclass.ismother,
            mergeclass.code AS mothercode,
            mergeclass.id AS mothercodeid,
            mergeclass.slots AS mothercodeslots,
            mainclass.mergein,
            mainclass.inst,
            instructor.lname,
            instructor.fname,
            instructor.mname,
            instructor.suffix
        FROM
            class AS mainclass
            Left Join enrolldet ON mainclass.id = enrolldet.class
            Left Join enroll ON enrolldet.enrollno = enroll.enrollno
            Inner Join period ON mainclass.period = period.id
            Inner Join section ON mainclass.section = section.id
            Inner Join subject ON mainclass.subject = subject.id
            Left Join sched ON mainclass.sched = sched.id
            Left Join class AS mergeclass ON mainclass.mergein = mergeclass.id
            Left Join instructor ON mainclass.inst = instructor.userid
            Left Join course ON section.course = course.id
         WHERE 
            (period.id = :period OR period.code = :period)";
if($level != ''){
    $str .= " AND course.level = '".$level."'";
}
if($dept != ''){
    $str .= " AND course.dept = '".$dept."'";
}
if($display != ''){
    switch ($display) {
        case 'open':
            $str .= " AND mainclass.slots > assessedinclass";
            break;
        case 'dissolved':
            $str .= " AND mainclass.dissolved = 1";
            break;
        case 'tutorial':
            $str .= " AND mainclass.tutorial = 1";
            break;
        case 'closed':
            $str .= " AND mainclass.slots <= assessedinclass";
            break;
    }       
}            
$str .= "GROUP BY
            mainclass.id,
            mainclass.code";

$str .="HAVING <your condition>";

$str .= " ORDER BY subject.code, mainclass.id";
return $this->_db->select($str,array(':period' => $period)); 

Answer 2

Вы можете попробовать ниже.Напишите внешний выбор, в котором будут все необходимые столбцы для обработки фильтров.

select
    classid,
    classcode,
    assessedinclass,
    validatedinclass,
    sectionname,
    subcode,
    subdesc,
    units,
    schedule,
    tutorial,
    dissolved,
    slots,
    ismother,
    mothercode,
    mothercodeid,
    mothercodeslots,
    mergein,
    inst,
    lname,
    fname,
    mname,
    suffix 
from 
    (select
         mainclass.id AS classid,
         mainclass.code AS classcode,
         Sum(case when enroll.acctok = '1' and enroll.assessed = '1'
                    then enroll.assessed 
                    else 0 
             end) as assessedinclass,
         Sum(enroll.validated = '1') AS validatedinclass,
         section.name AS sectionname,
         subject.code AS subcode,
         subject.subdesc,
         mainclass.units,
         sched.name AS schedule,
         mainclass.tutorial,
         mainclass.dissolved,
         mainclass.slots,
         mainclass.ismother,
         mergeclass.code AS mothercode,
         mergeclass.id AS mothercodeid,
         mergeclass.slots AS mothercodeslots,
         mainclass.mergein,
         mainclass.inst,
         instructor.lname,
         instructor.fname,
         instructor.mname,
         instructor.suffix
     from
         class as mainclass
     left join 
         enrolldet on mainclass.id = enrolldet.class
     left join 
         enroll on enrolldet.enrollno = enroll.enrollno
     inner join 
         period on mainclass.period = period.id
     inner join 
         section on mainclass.section = section.id
     inner join 
         subject on mainclass.subject = subject.id
     left join 
         sched on mainclass.sched = sched.id
     left join 
         class as mergeclass on mainclass.mergein = mergeclass.id
     left join 
         instructor on mainclass.inst = instructor.userid
     left join 
         course on section.course = course.id)
where
    (period.id = :period OR period.code = :period);

Ваш последний запрос будет -

select
    <req_cols> 
 from
     (select 
          <agg_cols> 
      from 
          table 
      group by 
          <grpCols>)
where 
    <filter on agg cols>