Question

我的请求中有问题：

SELECT regionn, COUNT(regionn) AS total,
COUNT(last_date_o) AS ouvreurs,
COUNT(last_date_o)*100/COUNT(regionn) AS ratio,
COUNT(gender='mr'), COUNT(gender='mme')
FROM data WHERE length(regionn)=2
GROUP BY regionn ORDER BY regionn ASC

性别列有两个可能的值：＆＃39; mr＆＃39;或者＆＃39; mme＆＃39;。使用COUNT（性别=＆＃39; mr＆＃39;），COUNT（性别=＆＃39; mme＆＃39;）我想要每个的总数，但返回相同的值。

事实上COUNT（性别=＆＃39; mr＆＃39;），COUNT（性别=＆＃39; mme＆＃39;）与COUNT（性别），COUNT（性别）......完全相同/ p>

我该怎么做？

感谢您的帮助

Answer 1

COUNT不是正确的聚合器，您应该使用SUM。

实际上COUNT(gender='mr')，COUNT(gender='mme')与COUNT(gender)完全相同

这是因为COUNT计算了不是NULL的任何内容，而SUM会将1和0加起来。

SELECT
    regionn
,   COUNT(regionn) AS total
,   COUNT(last_date_o) AS ouvreurs\
,   COUNT(last_date_o)*100/COUNT(regionn) AS ratio
,   SUM(CASE WHEN gender='mr' THEN 1 ELSE 0 END) AS mrs
,   SUM(CASE WHEN gender='mme' THEN 1 ELSE 0 END) AS mmes
FROM data
WHERE length(regionn)=2
GROUP BY regionn
ORDER BY regionn ASC

Answer 2

试试这个：

SELECT regionn, 
COUNT(regionn) AS total,
COUNT(last_date_o) AS ouvreurs,
COUNT(last_date_o)*100/COUNT(regionn) AS ratio,
COUNT(gender='mr' or null), 
COUNT(gender='mme' or null)
FROM data WHERE length(regionn)=2
GROUP BY regionn ORDER BY regionn ASC

COUNT(gender='mr' or null)的解释：

gender == mr

count(gender='mr' or null) =＆gt; count('mr'='mr' or null) =＆gt; count(true or null) =＆gt; count(true) =＆gt; 1

gender == mme

count(gender='mr' or null) =＆gt; count('mme'='mr' or null) =＆gt; count(false or null) =＆gt; count(null) =＆gt; 0

这个技巧使用了true or null == true和false or null == null

这一事实

COUNT中的条件子句

2 个答案: