选择涉及日期和时间比较的查询

Question

Here is my MS Sql table.. Table: http://snag.gy/L6ag1.jpg

SELECT 
    * 
FROM Table1 
WHERE   
    Class = '12' 
    AND Section = 'B' 
    AND '3/4/2013' BETWEEN DATE AND TODATE 
    and '3/14/2013' between Date and ToDate 
    or '3/4/2013' < Date and '3/14/2013' > ToDate 
    AND (
            '12:00 PM'  between [StartTime] and endtime 
            and '1:00 PM' between [StartTime] and endtime 
            or ('12:00 PM' < StartTime and '1:00 PM' > EndTIme)
        )

The above query is returning all the 6 rows of the table while the below query returns 0 rows..

SELECT 
    * 
FROM Teacher 
WHERE   
    Class = '12' 
    AND Section = 'B' 
    and '12:00 PM'  between [StartTime] and endtime 
    and '1:00 PM' between [StartTime] and endtime 
    or ('12:00 PM' < StartTime and '1:00 PM' > EndTIme)

I was expecting the query at the top to return 0 rows since i used AND operand, so even if the date comparison returns rows the combined query shouldnt return anything since time comparison returns false.

SCRIPT TO CREATE TABLE:

INSERT INTO [SLIITComDB].[dbo].[Teacher]
           ([TeacherId]
           ,[TeacherName]
           ,[Class]
           ,[Section]
           ,[SubjectId]
           ,[Date]
           ,[ToDate]
           ,[Day]
           ,[StartTime]
           ,[EndTIme]
           ,[Absent])
     VALUES
           (<TeacherId, int,>
           ,<TeacherName, varchar(50),>
           ,<Class, varchar(50),>
           ,<Section, varchar(50),>
           ,<SubjectId, varchar(50),>
           ,<Date, date,>
           ,<ToDate, date,>
           ,<Day, varchar(50),>
           ,<StartTime, time(7),>
           ,<EndTIme, time(7),>
           ,<Absent, varchar,>)
GO

Answer 1

In SQL, AND operator has precedence over OR operator.

So in your first query, the conditions look like this:

WHERE   
  ( Class = '12' 
    AND Section = 'B' 
    AND '3/4/2013' BETWEEN DATE AND TODATE 
    and '3/14/2013' between Date and ToDate
   ) OR (
    '3/4/2013' < Date and '3/14/2013' > ToDate 
    AND (
            '12:00 PM'  between [StartTime] and endtime 
            and '1:00 PM' between [StartTime] and endtime 
            or ('12:00 PM' < StartTime and '1:00 PM' > EndTIme)
        ))

The result is TRUE when either of the top or bottom sections (separated by OR ) are TRUE .

The conditions in your second query also look like:

WHERE   
  ( Class = '12'
    AND Section = 'B' 
    and '12:00 PM'  between [StartTime] and endtime 
    and '1:00 PM' between [StartTime] and endtime
   )
    or ('12:00 PM' < StartTime and '1:00 PM' > EndTIme)

You first query can return result even if time comparisions are all FALSE because your first two date comparisions can be TRUE .

Answer 2

Actually it is your OR which causes this:

The first part before the or is true according to your data. So these will be returned. Add brackets to clarify things.

True:

 Class = '12' 
    AND Section = 'B' 
    AND '3/4/2013' BETWEEN DATE AND TODATE 
    and '3/14/2013' between Date and ToDate 

 OR

False:

'3/4/2013' < Date and '3/14/2013' > ToDate 
    AND (
            '12:00 PM'  between [StartTime] and endtime 
            and '1:00 PM' between [StartTime] and endtime 
            or ('12:00 PM' < StartTime and '1:00 PM' > EndTIme)
        )

Try this simplified :

select * 
from Table1 
where 1 = 1
or 2 = 2
and 1 = 3