Question

现在我想计算列包含值或不为null的行。我是SQL的初学者;我的SQL查询如下：

select count(news) AS news_count, count(`msg`) as msg_count , count('req') as req_count 
from news_msg_activity 
where news!='' 
UNION 
select count(news) AS news_count, count(`msg`) as msg_count , count('req') as req_count 
from news_msg_activity 
where msg!='' 
UNION  
select count(news) AS news_count, count(`msg`) as msg_count , count('req') as req_count  
from news_msg_activity 
where req!=''

当我运行查询时，它会在结果中给出两个数字。但我需要一个数字结果，它将计算上述操作中的记录数。我不知道如何编写该查询。有人能帮助我吗？

但我需要

news_count || msg_count || req_count                          
    2      ||     2     ||    3

Answer 1

将查询包装在子查询中。

SELECT * -- here you can sum, count or whatever elese you need
FROM (
  -- your query goes here
) as src

或者只是

select 
    sum(news!='') AS news_count
    , sum( msg!='' ) as msg_count 
    , sum(req!='') as req_count 
from news_msg_activity

as boolean语句将整数计算为0/1（false / true） - 这将作为满足条件的计数。

检查小提琴：http://sqlfiddle.com/#!9/8c780/1

Answer 2

COUNT(column)已经返回非空记录的数量，因此，除非我误解了您尝试做的事情，否则您可以更加简单。以下查询应返回每个字段的非空记录数：

select count(news) AS news_count
, count(`msg`) as msg_count
, count(req) as req_count 
from news_msg_activity

如果你担心的是从计数中删除空字符串，你可以使用NULLIF函数：

select count(nullif(news, '')) AS news_count
, count(nullif(`msg`, '')) as msg_count
, count(nullif(req, '')) as req_count 
from news_msg_activity

Answer 3

你确定你真的需要UNION吗？也许是这样的？

SELECT 
    *
FROM
    (SELECT 
        count(news) AS news_count
    FROM
        news_msg_activity 
    WHERE
        news!= '') a,
    (SELECT 
        count(msg) as msg_count
    FROM
        news_msg_activity 
    WHERE
        msg!= '') b,
    (SELECT 
        count(req) as req_count
    FROM
        news_msg_activity 
    WHERE
        req!= '') c

此外，在表的方案中创建字段news, msg, req - NOT NULL。因为现在count（）计算具有字段空值的行。您可以添加IS NOT NULL进行查询，但更好的解决方案是在表格的方案中设置NOT NULL并设置默认值。这将使你免于错误＆＃34;将来。

Sql Count包含一些值的行

3 个答案: