在mysql查询本身中获取行数答案

【问题标题】：obtain row count in mysql query itself在mysql查询本身中获取行数
【发布时间】：2010-11-22 02:30:30
【问题描述】：

我想在查询本身中获取子查询的返回行数。然后我将在 if 情况下在主查询中使用它。我添加了一个示例，作为一个虚拟字符串，我输入了 QUERY_ROW_COUNT。是否有任何功能可以实现这一点？在此先感谢...问候...

SELECT period_id, 
       lt_id, 
       period_name, 
       min_stay, 
       IF(QUERY_ROW_COUNT=1, 1,0) as tag 
  FROM (SELECT period_id, 
               lt_id, 
               period_name, 
               min_stay, 
               fromDate, 
               toDate, 
               DATEDIFF( '2010-12-27', '2010-12-10' ) as totalDays, 
               nightly_rate,
               case when ('2010-12-10' > fromDate AND '2010-12-27' < toDate) then  
                  DATEDIFF( '2010-12-27', '2010-12-10' )  
                  else 0 
               end as d6,
               case when ('2010-12-10' > fromDate AND '2010-12-27' > toDate) then 
                  DATEDIFF( toDate, '2010-12-10' )+1 
                  else 0 
               end as d7,
               case when ('2010-12-10' < fromDate AND '2010-12-27' < toDate) then 
                  DATEDIFF( '2010-12-27', fromDate ) 
                  else 0 
               end as d8,
               case when ('2010-12-10' < fromDate AND '2010-12-27' > toDate) then 
                  DATEDIFF( toDate, fromDate ) 
                  else 0 
               end as d9    
          FROM `lt_hperiods`
         WHERE ('2010-12-10' BETWEEN Date( fromDate ) AND Date( toDate )  ) 
            OR ( '2010-12-27' BETWEEN Date( fromDate ) AND Date( toDate ))
            OR ('2010-12-10' <= fromDate  AND  '2010-12-27' >= toDate )
           AND (lt_id=1)) MQS

【问题讨论】：

标签： sql mysql aggregate-functions

【解决方案1】：

您可以在主from 子句的内联选择中使用count( 1 ) as some_variable，然后在主查询的选择中将其称为MQS.some_variable。

【讨论】：

【解决方案2】：

您是否尝试过 COUNT(*) 或 COUNT(DISTINCT period_id)，其中有 QUERY_ROW_COUNT？

【讨论】：

【解决方案3】：

（已解决...这是正在扫描工作解决方案的标签：）感谢所有建议。我忘了写我已经尝试过所有的求和和计数函数。但是我解决了我的问题......我希望这对某人有帮助。 mysql允许您定义很棒的动态变量..这是参考：

http://www.xaprb.com/blog/2006/12/02/how-to-number-rows-in-mysql/

这是代码：

set @countT = 0;
set @rowCount = 0;

SELECT MQ.period_id, MQ.lt_id, MQ.period_name, MQ.min_stay, MQ.fromDate, MQ.toDate, MQ.nightly_rate, MQ.periodDays, 
MQ.totalDays,
@countT := if(@countT = MQ.periodDays, 0 , @countT + MQ.periodDays) as periodDaysTotal, 
@rowCount:= @rowCount +1
FROM (
SELECT period_id, lt_id, period_name, min_stay, fromDate, toDate, totalDays, nightly_rate, (d1+d2+d3+d4+d5+d6+d7+d8+d9) periodDays 

FROM

(SELECT period_id, lt_id, period_name, min_stay, fromDate, toDate, DATEDIFF( '2010-05-02', '2010-03-10' ) as totalDays,  nightly_rate,

 case when ('2010-03-10' > fromDate AND '2010-05-02' < toDate) then DATEDIFF( '2010-05-02', '2010-03-10' ) else 0    end as d6,
 case when ('2010-03-10' > fromDate AND '2010-05-02' > toDate) then DATEDIFF( toDate, '2010-03-10' ) else 0  end as d7,
 case when ('2010-03-10' < fromDate AND '2010-05-02' < toDate) then DATEDIFF( '2010-05-02', fromDate ) else 0 end as d8,
 case when ('2010-03-10' < fromDate AND '2010-05-02' > toDate) then DATEDIFF( toDate, fromDate ) else 0 end as d9

 FROM `lt_hperiods`
 WHERE  
 ('2010-03-10' BETWEEN Date( fromDate ) AND Date( toDate )  ) OR
 ( '2010-05-02' BETWEEN Date( fromDate ) AND Date( toDate ))
 OR ('2010-03-10' <= fromDate  AND  '2010-05-02' >= toDate )
AND (lt_id=1)
) MQS ) MQ

【讨论】：