mysql - 如果没有记录，我怎么能算作 0？

Question

我有这样的问题

select `temp`, IfNULL(count(id),0) t 
from survey 
where `temp`<>'NULL' and `temp`<> '' and date(submitdate)='date' 
group by `temp

有 o/p

temp        t
A1          1

但如果没有记录，则在所选日期会发生以下情况:我没有得到任何结果。答案像 A1,A2,A3

我需要这样的o/p

temp   t
A1     1
A2     0
A3     0

Answer 1

您将不得不使用一些自JOIN 技巧来获取每个答案的记录:

SELECT s.`temp`, count(survey.id) t
-- This will ensure that you will get all relevant answers A1, A2, A3
FROM (
  SELECT DISTINCT `temp`
  FROM survey
  WHERE `temp` <> 'NULL' and `temp` <> ''
--             ^^^^^^^^^ Might want to replace this by `temp` IS NOT NULL?
) s
-- Only then, you will actually get the actual records per answer and date
LEFT OUTER JOIN survey
  ON s.`temp` = survey.`temp`
  AND date(survey.submitdate) = 'date'
GROUP BY s.`temp`

请确保您在 survey.temp 上有一个索引。