是否可以在同一查询的 WHERE 子句中使用子查询结果作为条件。我有这个sql代码。我想比较子查询中的结果 ASSESSEDINCLASS 和 C.SLOTS 以确定插槽是否已满。这甚至可以在单个查询中实现吗?提前致谢
$str = "SELECT
c.id,
c.code AS classcode,
section.name AS sectionname,
subject.code,
subject.subdesc,
c.units,
sched.name AS schedule,
c.slots,
c.dissolved,
c.tutorial,
c.inst,
instructor.lname,
instructor.fname,
instructor.mname,
instructor.suffix,
(SELECT
Count(e.enrollno)
FROM
enrolldet AS e
Inner Join enroll ON e.enrollno = enroll.enrollno
Inner Join class ON e.class = class.id
WHERE
enroll.validated = '1' AND
class.id = c.id) as validatedinclass,
(SELECT
Count(e.enrollno)
FROM
enrolldet AS e
Inner Join enroll ON e.enrollno = enroll.enrollno
Inner Join class ON e.class = class.id
WHERE
enroll.assessed = '1' AND
class.id = c.id) as assessedinclass,
(SELECT
q.id
FROM
merged
Inner Join class AS q ON merged.mothercode = q.id
WHERE
merged.mergefrom = c.id) AS mergedto_mothercode
FROM
class AS c
Left Join sched ON c.sched = sched.id
Left Join section ON c.section = section.id
Left Join subject ON c.subject = subject.id
Left Join instructor ON c.inst = instructor.userid
Left Join course ON section.course = course.id
Inner Join period ON c.period = period.id
WHERE
(period.id = '".$period."' OR period.code = '".$period."')";
if($status == 'open'){
$str .= " AND c.slots < assessedinclass";
}
$str .= " ORDER BY subject.subdesc";
最佳答案
要回答你的问题,是的,你可以使用 Having
子句,让你在 where
子句之后使用它
having assessedinclass = someval
或者
$str .= " HAVING c.slots < assessedinclass";
但我更喜欢不要使用依赖子查询,而是将这些作为子句连接到您的主查询中,如下所示
SELECT ....,
COALESCE(aic.assessedinclass, 0) AS assessedinclass,
FROM class AS c
JOINS....
LEFT JOIN (SELECT class.id,
COUNT(e.enrollno) AS assessedinclass
FROM enrolldet AS e
INNER JOIN enroll
ON e.enrollno = enroll.enrollno
INNER JOIN class
ON e.class = class.id
WHERE enroll.assessed = '1'
GROUP BY class.id) aic
ON aic.id = c.id
WHERE ( period.id = '".$period."' OR period.code = '".$period."' )
AND c.slots < COALESCE(aic.assessedinclass, 0)
关于php mysql 在同一查询中的 WHERE 子句中使用子查询结果,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/50830063/