Question

SELECT NAMA_DUN, 
COUNT(case when ((RIGHT(noMyKid, 1))% 2) = 0 then 1 else 0 end) AS FEMALE, 
COUNT(case when ((RIGHT(noMyKid, 1))% 2) = 1 then 1 else 0 end) AS MALE, 
COUNT(DISTINCT(noMyKid)) as jumlah
FROM mohon
LEFT JOIN dun ON dun.KOD_DUN=mohon.dun_nama
WHERE status_proses =  'diproses'
AND concat('20', substr(noMyKid, 1, 2)) = '2008'
AND status_mohon =  'Layak'
AND status_semak =  '1'
AND (
status_bayar =  ''
OR status_bayar =  'Belum'
OR status_bayar =  'Sudah')
AND (
status_terima =  ''
OR status_terima =  'Terima'
) GROUP BY dun_nama
ORDER BY NAMA_DUN

这是我的mysql代码。为什么我的“COUNT CASE WHEN”为女性和男性专栏提供相同的输出。

Answer 1

通常COUNT()用于计算行数，因此通常以COUNT(*)的形式使用。当您使用字段（或其他任何内容）作为COUNT()的参数时，对于每个无NULL值，它都会计为1。

在您的情况下，您的所有值都不是NULL（它们是1或0），因此您最终会得到相同的结果。

所以Abhik Chakraborty是对的，使用SUM()，一切都应该没问题。

Answer 2

COUNT()函数只识别非空值，因此当使用像这里一样的case表达式时，可以在需要的地方显式返回NULL

SELECT NAMA_DUN, 
COUNT(case when ((RIGHT(noMyKid, 1))% 2) = 0 then 1 else NULL end) AS FEMALE, 
COUNT(case when ((RIGHT(noMyKid, 1))% 2) = 1 then 1 else NULL end) AS MALE, 
COUNT(DISTINCT(noMyKid)) as jumlah

OR，通过忽略else条件隐式返回NULL

SELECT NAMA_DUN, 
COUNT(case when ((RIGHT(noMyKid, 1))% 2) = 0 then 1 end) AS FEMALE, 
COUNT(case when ((RIGHT(noMyKid, 1))% 2) = 1 then 1 end) AS MALE, 
COUNT(DISTINCT(noMyKid)) as jumlah

OR，使用SUM（）模拟计数的效果，前提是你使用1和0（或1和NULL）

SELECT NAMA_DUN, 
SUM(case when ((RIGHT(noMyKid, 1))% 2) = 0 then 1 else 0 end) AS FEMALE, 
SUM(case when ((RIGHT(noMyKid, 1))% 2) = 1 then 1 else 0 end) AS MALE, 
COUNT(DISTINCT(noMyKid)) as jumlah

使用mysql的COUNT数据使用案例

2 个答案: