Combine Two Date Fields


I have two tables with date fields. Table1 has the date formatted like this: 2013-03-31 13:01:00. Table2 the date is formated like this 2013-03-31. How can I combine the two tables?

SELECT   Table1.ArrivalDateTime, Table2.MeetingDate
FROM         Table1 INNER JOIN
                      Table2 ON (CONVERT(date, Table1.ArrivalDateTime, 101) = Table2.MeetingDate

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PaulConnect With a Mentor Commented:
        , Table2.MeetingDate
FROM Table1
INNER JOIN Table2 ON CONVERT(DATE, Table1.ArrivalDateTime) = Table2.MeetingDate

You do not need the ,'101'

The only concern here is that applying a function to the datetime field may remove use of indexing you may have on ArrivalDateTime. Opinions differ on this e.g. (see this forum)
Does SQL 2008 also have an optimization such that
Where convert(date, aDateTimeColumn) = '20101020'
will get optimized to an INDEX SEEK rather than an scan?

Yes, it can do a SEEK for above operation.
Tibor Karaszi, SQL Server MVP
I would suggest you inspect the execution plan to see if it is causing table or index scanning.

& some semantics (sorry):

you have 2 fields, one appears to be datetime, the other appears to be date
date and datetime fields are seen in a format - but not stored in a format - hence what they look like doesn't really matter. What does matter is the actual data type of each field.

oh, and an alternative to using convert(date,....) which is efficient is:
        , Table2.MeetingDate
FROM Table1
INNER JOIN Table2 ON dateadd(day, datediff(day,0, Table1.ArrivalDateTime ), 0) = Table2.MeetingDate

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the combination of datediff with dateadd strips time to 00:00:00

the notes above regarding indexing still apply of course.
{+2 edits sorry}
Surendra NathTechnology LeadCommented:
you can write it as below

SELECT   Table1.ArrivalDateTime, Table2.MeetingDate
FROM         Table1 
INNER JOIN   Table2 
ON DATEDIFF(dd,Table1.ArrivalDateTime,Table2.MeetingDate) = 0

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Ephraim WangoyaCommented:
That join is really not good, what if you have multiple arrivals and meetings on the same day.
Your result set will be invalid.
You need to create primary and foreign keys on your tables to implement the join
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select table2.arrivaldatetime, table2.meetingdate from table1 inner join table2
on cast(floor(cast(table1.arrivaldatetime as float) ) as datetime) = table2.meetingdate
RecipeDanAuthor Commented:
Awkingoo your suggestion shows as 2013-02-06 00:00:00.000. I need to delete the time in order to join the tables.
SharathData EngineerCommented:
Do you just want to join on dates? Whats wrong with your query?
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