可以使用MySQL，IFNULL（）返回列值爲int的字符串嗎？

我查詢可以使用MySQL，IFNULL（）返回列值爲int的字符串嗎？

select cname, count(screening_occapancy.idclient) as 'Count' 
from client, screening_occapancy 
where client.client_no = screening_occapancy.idclient 
group by cname

返回如下：

Name  Count 
Name1  2 
Name2  3 
Name3  6

等，現在我想在「計數」被「找不到」如果值爲null或0的值，是可能？我需要在我的結果類似的東西：

Name  Count 
    Name1   2 
    Name2   3 
    Name3 "Not found"

來源

2016-06-11 Gilzy

標題問題的答案是肯定的：'ifnull（column，「Not Found」）' – Barmar

Select cname , 
case when Count is null or count =0 then 'Not found' 
else Count end as count 
from 
    (select cname, 
count(screening_occapancy.idclient) as 'Count' 
    from client left join screening_occapancy 
    on 
    client.client_no = screening_occapancy.idclient group by cname) t

編寫一個包裝查詢查詢上述檢查數列

來源

2016-06-11 16:23:50

Working。非常感謝。 – Gilzy

不客氣@Gilzy –

使用left join獲得0所有未找到匹配

select c.cname, 
     count(so.idclient) as 'Count' 
from client c 
left join screening_occapancy so on c.client_no = so.idclient 
group by c.cname

而且BTW不使用傳統的隱含了連接語法。使用顯式連接。

來源

2016-06-11 16:23:39

select cname, IF(count(screening_occapancy.idclient)!=0,count(screening_occapancy.idclient),'NOT FOUND') as 'Count' 
from client, screening_occapancy 
where client.client_no = screening_occapancy.idclient 
group by cname

，或者如果計數返回null？

select cname, IFNULL(count(screening_occapancy.idclient),'NOT FOUND') as 'Count' 
from client, screening_occapancy 
where client.client_no = screening_occapancy.idclient 
group by cname

來源

2016-06-11 17:34:37 PawelN

可以使用MySQL，IFNULL（）返回列值爲int的字符串嗎？

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