Question

我有这个查询，它显示了一些属性，并从另一个表中计算对它的引用数量：

SELECT 
       p.id,p.propName
       (
         SELECT COUNT(*) FROM propLoc WHERE propLoc.propID = p.id
       ) AS number
FROM property as p 
WHERE p.category != 'natural'

这会生成一个包含我想要过滤的所有信息的好表：

id | propName | number
3  | Name 1   | 3
4  | Name 2   | 1
5  | Name 3   | 0
6  | Name 4   | 10
etc etc

我现在想要过滤掉数字＆lt; = 0的属性所以我尝试添加AND number > 0但它会对Unknown column 'number' in 'where clause'作出反应，显然你不能过滤子查询指定的名称？

如何实现目标？

Answer 1

试试这个::

SELECT 
       p.id,p.propName, count(1) as number
FROM property as p 
inner join propLoc on (propLoc.propID = p.id)
WHERE p.category != 'natural'
group BY p.id

Answer 2

您拥有的内联子查询等同于LEFT JOIN。将您的查询重写为Join，并将其设为INNER。这样：

SELECT p.id
     , p.propName
     , grp.number
FROM property AS p 
  INNER JOIN 
     ( SELECT propID 
            , COUNT(*) AS number
       FROM propLoc
       GROUP BY propID
     ) AS grp 
    ON grp.propID = p.id
WHERE p.category <> 'natural' ;

或者这个：

SELECT p.id
     , p.propName
     , COUNT(*) AS number
FROM property AS p 
  INNER JOIN propLoc 
    ON propLoc.propID = p.id
WHERE p.category <> 'natural' 
GROUP BY p.id ;

Answer 3

当WHERE不起作用时，HAVNING起作用，因为它会在链中稍后过滤结果

SELECT 
       p.id,p.propName
       (
         SELECT COUNT(*) FROM propLoc WHERE propLoc.propID = p.id
       ) AS number
FROM property as p 
WHERE p.category != 'natural'
HAVING number > 0

Answer 4

SELECT p.id,p.propName,count(p.id) as number
FROM property as p 
inner join propLoc prop WHERE prop.propID = p.id
WHERE p.category != 'natural'
group p.id;

OR

SELECT p.id,p.propName,count(p.id) as number
FROM property as p 
left join propLoc prop WHERE prop.propID = p.id
WHERE p.category != 'natural' and number > 0
group p.id;

Answer 5

SELECT 
       p.id,p.propName,q.number
       from
       (
         SELECT propID,COUNT(*) as number FROM propLoc WHERE propLoc.propID = p.id
       ) q join
 property as p 
on q.propID=p.id
 where p.category != 'natural'

where子句由子查询定义的字段

5 个答案: