How to get minimum date by each records from multiple records

Question

I would like to get the minimum date of each record in my table having multiple entry of date with one primary key. Take a look at my table:

   CaseNo     Entry_         


        

Answer 1

Unsure what RDBMS you're using, but two approaches come to mind.

JOIN against derived table

Create a derived table of (CaseNo, MIN(Entry_date)) rows, and join that against your primary table:

    SELECT CaseNo, Entry_date, d.Min_date AS "Min_date"
      FROM tbl
INNER JOIN (  SELECT CaseNo, MIN(Entry_date) AS "Min_date"
                FROM tbl
            GROUP BY 1) d
        ON tbl.CaseNo = d.CaseNo;

Use analytic (window) functions

If your RDBMS supports it, you can skip the derived table and ask for your records with the minimum Entry_date by CaseNo provided by the system:

SELECT CaseNo, Entry_date, MIN(Entry_date) OVER (PARTITION BY CaseNo) AS "Min_date"
  FROM tbl;