Finding Max/Min Value In A Column When Row Data Repeat

I have a table. In that table I have a list by student number that lists the entry dates into a particular grade. When trying to list only the first time entered, there is no unique way to identify one row from another other than the date. Is there a way to use max or min to only pull one date per student number? I have done a series of case when statements and I am able to get it down to 1 to 2 entries per student number, but I need to get it down to only 1 date per student number.

Thank you for your help






SELECT DISTINCT mx.stu_num,

CASE WHEN er.STU_NUM = ep.STU_NUM

THEN er.enterdater

ELSE CASE WHEN ea.STU_NUM = ep.STU_NUM

THEN ea.enterdatea

ELSE CASE WHEN eb.STU_NUM = ep.STU_NUM

THEN ep.enterdatep

ELSE eb.enterdateb

END

END

END AS entrydate


FROM dbo.mx AS mx LEFT OUTER JOIN

dbo.v_EntryDate9_R AS er ON mx.stu_num = er.stu_num LEFT OUTER JOIN

dbo.v_EntryDate9_P AS ep ON mx.stu_num = ep.stu_num LEFT OUTER JOIN

dbo.v_EntryDate9_A AS ea ON mx.stu_num = ea.stu_num LEFT OUTER JOIN

dbo.v_EntryDate9_B AS eb ON mx.stu_num = eb.stu_num