Question

I have 2 tables, CustomerMaster, EntBookings, now for each customer, I have record of each of their booking(s) in EntBookings table.
What I want is, to find out the first date of booking for all customers.

What I tried,

SELECT cm.CustomerCode,
       cm.CustomerName,
       MIN(eb.BookingDate) OVER(PARTITION BY eb.BookingByCustomer)
FROM   EntBookings eb
       INNER JOIN CustomerMaster cm
            ON  cm.CustomerCode = eb.BookingByCustomer
GROUP BY
       cm.CustomerCode,
       cm.CustomerName,
       eb.BookingByCustomer,
       eb.BookingDate 

It gives the result as

Cust1   ABC     2013-01-24 00:00:00.000
Cust2   ABCD    2013-01-24 00:00:00.000
Cust2   ABCD    2013-01-24 00:00:00.000
Cust3   BCD     2013-01-25 00:00:00.000
Cust4   BCDE    2013-01-24 00:00:00.000
Cust7   DEF     2013-01-02 00:00:00.000

I don’t know why for Cust2, its showing 2 rows? How can I get it to return just one row?

If I do this..

SELECT cm.CustomerCode,
       cm.CustomerName,
       MIN(eb.BookingDate) OVER(PARTITION BY eb.BookingDate)
FROM   EntBookings eb
       INNER JOIN CustomerMaster cm
            ON  cm.CustomerCode = eb.BookingByCustomer
GROUP BY
       cm.CustomerCode,
       cm.CustomerName,
       eb.BookingByCustomer,
       eb.BookingDate 

I get this…

Cust7   DEF     2013-01-02 00:00:00.000
Cust1   ABC     2013-01-24 00:00:00.000
Cust2   ABCD    2013-01-24 00:00:00.000
Cust4   BCDE    2013-01-24 00:00:00.000
Cust3   BCD     2013-01-25 00:00:00.000
Cust2   ABCD    2013-02-13 00:00:00.000

In this case, though I am still getting 2 rows for Cust2, dates are wrong, it should be 2013-01-24 00:00:00.000 (as in first case), but that is returning 2 rows. So, both of these queries are incorrect. Can anyone help me figure out what I am doing wrong?

Answer 1

You are complicating things and you are grouping too much. It seems you only want to group on customer code and name.

SELECT 
     cm.CustomerCode, 
     cm.CustomerName, 
     MIN(eb.BookingDate) 
 FROM 
      EntBookings eb
 JOIN
      CustomerMaster cm     ON       
       cm.CustomerCode = eb.BookingByCustomer
 GROUP BY
       cm.CustomerCode, cm.CustomerName