php - where 子句中的 MYSQL 别名

Question

我有一个查询，我想在 WHERE 条件中使用别名列来过滤结果集，我读到您无法执行此操作，但我还没有其他方法可以有效地执行此操作，因为我正在处理数千条记录。

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

我尝试使用 ASSESSEDINCLASS 来过滤它，其中 mainclass.slots > ASSESSEDINCLASS 意味着主题是开放的

如果 mainclass.slots <= ASSESSEDINCLASS 它将被视为已关闭

Answer 1

您可以尝试以下。编写一个外部选择，其中包含处理过滤器所需的所有列。

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);

您的最终查询将是 -

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