MySQL BETWEEN and “>= AND <=” giving different results

Question

Is there any difference between MySQL BETWEEN operator and using ">= <="?

When i tried them on this query, they give different results.

SELECT 
      tblStaff.TitleGredCd,
      count(StudCourse1.StaffNoIC),     
      StudCourse1.StaffNoIC,
      StaffNm,
      BranchNm, 
      StDt, 
      EndDt, 
      SUM(datediff(EndDt,StDt)+1)  
      TotalDay, 
      (SELECT SUM( pembelajaranhour ) 
         FROM tblpembelajaran d 
         WHERE d.StaffNoIC = tblStaff.StaffNoIC
           AND YEAR( PembelajaranDate ) = 2011 )Totalhour,
      (SELECT SUM( datediff( kendiridate, kendiridate ) +1 ) 
         FROM tblkendiri d 
         WHERE d.StaffNoIC = tblStaff.StaffNoIC 
           AND YEAR( kendiridate ) = 2011 ) Totalkendiriday
   FROM 
      StudCourse1, 
      tblStaff 
         LEFT OUTER JOIN tblRefBranch 
            ON tblStaff.BranchCd = tblRefBranch.BranchCd, 
      tblRefTitleGred
   WHERE 
          StudCourse1.StaffNoIC = tblStaff.StaffNoIC 
      AND tblStaff.TitleGredCd = tblRefTitleGred.TitleGredCd 
     [Date Condition]
   GROUP BY 
      tblStaff.TitleGredCd, 
      StudCourse1.StaffNoIC

If I use AND StDt BETWEEN '2011-1-1' AND '2011-12-31' for [Date Condition] I get 6 returned results. But if I use AND StDt >= '2011-1-1' AND EndDt '2011-12-31' for [Date Condition] I get 7 returned results. Any advice would be greatly appreciated.

Answer 1

BETWEEN is a bit odd with DATE types. What you are saying with your date types is

// These 2 are the same
BETWEEN '2011-01-01' AND '2011-12-31'
BETWEEN '2011-01-01 00:00:00' AND '2011-12-31 00:00:00'

and so it only match up to '2011-12-30 23:59:59', or to put it another way on a DATE field it won't match '2011-12-30'.

When you search for '2011-01-01' <= .... <= '2011-12-31' it then correctly matches the date being potentially == '2011-12-31'

So you have 4 options. The first one is to add 1 day onto the upper bound. This is the option I usually utilise The BETWEEN plays very nicely with an index on the date column, and there's no CAST or DATE() used on the data rows as the ADDDATE('2011-12-31',1) only needs executing once

WHERE `StDt` BETWEEN '2011-01-01' AND ADDDATE('2011-12-31',1)

The second is to explicitly specify the timestamp

WHERE `StDt`BETWEEN '2011-01-01 00:00:00' AND '2011-12-31 23:59:59'

The third, as you've found, is to use <= and >=

WHERE `StDt` >= '2011-01-01' AND `StDt` <= '2011-12-31'

A fourth option that also seems to work is the following, but I still prefer the first method as it's the one I know works + doesn't require using CAST or DATE on every row

WHERE DATE(`StDt`) BETWEEN DATE('2011-01-01') AND DATE('2011-12-31')

I hope this is of help

Answer 2

AND StDt BETWEEN '2011-1-1' AND '2011-12-31'

Checks whether the value in the column StDt is between the two values.

AND StDt >= '2011-1-1' AND EndDt <= '2011-12-31'

Checks whether the value in StDt is GTE a value, and the value is EndDt is LTE a value.

The first uses the value of only one column, the second uses the values of two. So they will return different results, they are different conditions. The only way they would be the same is if the value of StDt was always equal to the value of EndDt for every row.

To mimic the behaviour of your first BETWEEN clause with GTE/LTE operators, you would do this:

AND StDt >= '2011-1-1' AND StDt <= '2011-12-31'

This should return the same set of results.

Answer 3

You can see more explain on reference on mysql

For best results when using BETWEEN with date or time values, use CAST() to explicitly convert the values to the desired data type. Examples: If you compare a DATETIME to two DATE values, convert the DATE values to DATETIME values. If you use a string constant such as '2001-1-1' in a comparison to a DATE, cast the string to a DATE.

I suggest you continue use <= and >= for more exact results