mysql日期过滤不起作用

Question

下面的sql工作正常，并返回90个记录按预期方式，并且计数是正确的，但是当在sql中添加日期过滤时，它只返回44行而不是90，但总计数是正确。

SQL不注日期的过滤：

sql without date filtering: 
SELECT 
t4.firstname, 
t1.category 
,COUNT(t3.catid) as days 
FROM category AS t1 
LEFT JOIN (SELECT 
      DISTINCT empid,t1.catid 
     FROM attendance AS t2 
     LEFT JOIN category AS t1 ON (t1.catid>0) 
     ) AS t2 
ON (t1.catid=t2.catid) 
LEFT JOIN attendance AS t3 ON (t2.empid=t3.empid AND t3.catid=t2.catid) 
left join employee t4 on t2.empId=t4.empid 
GROUP BY t2.empid,t2.catid 
ORDER BY t2.empid,t2.catid; 

与日期过滤：

SELECT 
t4.firstname, 
t1.category 
,COUNT(t3.catid) as days 
FROM category AS t1 
LEFT JOIN (SELECT 
      DISTINCT empid,t1.catid 
     FROM attendance AS t2 
     LEFT JOIN category AS t1 ON (t1.catid>0) 
     ) AS t2 
ON (t1.catid=t2.catid) 
LEFT JOIN attendance AS t3 ON (t2.empid=t3.empid AND t3.catid=t2.catid) 
left join employee t4 on t2.empId=t4.empid 
where 
date_format(dateIn, '%Y-%m-%d')>=str_to_date("1/01/2015", '%m/%d/%Y') 
and date_format(dateout, '%Y-%m-%d')<=str_to_date("12/31/2015", '%m/%d/%Y') 
GROUP BY t2.empid,t2.catid 
ORDER BY t2.empid,t2.catid; 

Answer 1

当使用date_format您比较字符串，这样一切都越来越混乱。我建议你使用between而不是像date_field BETWEEN '2015-01-01' AND '2015-12-31'这样的两个条件，并坚持YYYY-MM-DD格式。

SELECT 
t4.firstname, 
t1.category 
,COUNT(t3.catid) as days 
FROM category AS t1 
LEFT JOIN (SELECT 
      DISTINCT empid,t1.catid 
     FROM attendance AS t2 
     LEFT JOIN category AS t1 ON (t1.catid>0) 
     ) AS t2 
ON (t1.catid=t2.catid) 
LEFT JOIN attendance AS t3 ON (t2.empid=t3.empid AND t3.catid=t2.catid) 
left join employee t4 on t2.empId=t4.empid 
where 
dateIn between '2015-01-01' and '2015-12-31' 
GROUP BY t2.empid,t2.catid 
ORDER BY t2.empid,t2.catid;