how to get multiple min values from two SQL tables? - sql-server

Question

I have two tables, a Members table and a Plan table. They are structured as follows.
member start_date Mplan Pplan version start_dt end_dt
John 20120701 johnplan johnplan 1 20120601 20130531
John 20130201 johnplan johnplan 2 20130601 20140531
John 20130901 johnplan
John 20131201 johnplan
I need to update the start_date on the Members table to be the minimum value present for that member but within the same Plan version.
Example:
20130201 would be changed to 20120701 and 20131201 would change to 20130901.
Code:
UPDATE Members
SET start_date =(
SELECT MIN(start_date) FROM Members a
LEFT JOIN Plan ON Mplan = Pplan AND
start_date BETWEEN start_dt AND end_dt
WHERE member=a.member
AND start_date BETWEEN start_dt AND end_dt
)
Unfortunately this sets every single start_date to 19900101 aka the lowest value in the entire table for that column.

Answer 1

First you need to get the minimum start date of each member for a specific plan. The following will provide you that.
select MIN(start_date) as min_date,a.member as member_name,a.Mplan as plan_name FROM Members a inner JOIN [plan] p ON a.Mplan = p.Pplan AND
start_date BETWEEN p.start_dt AND p.end_dt
group by a.member, a.Mplan
The result will be something like this.
min_date member_name plan_name
2012-07-01 00:00:00.000 John johnplan1
2013-09-01 00:00:00.000 John johnplan2
Use this to update each member's start date for a plan with the lowest start date of the respective plan.
update members
set start_date= tbl.min_date from
(SELECT MIN(start_date) as min_date,a.member as member_name,a.Mplan as plan_name FROM Members a
inner JOIN [plan] p ON a.Mplan = p.Pplan AND
start_date BETWEEN p.start_dt AND p.end_dt
group by a.member, a.Mplan) as tbl
where member=tbl.member_name and Mplan=tbl.plan_name
I created your 2 tables, members and plan, and tested this solution with sample data and it works. I hope it helps.

Answer 2

You really need to convert the dates to Datetime. You will have a greater precision, the possibility to store hours, days and minutes as well as access to date specific functions, international conversion and localization.
If your column is a Varchar(8), then it uses no less space than a Datetime column.
That said, what you are looking for is row_number().
Something like:
SELECT Member, MPlan, Start_Date, Row_Number() OVER (PARTITION BY Member, MPLan ORDER BY Start_Date) as Version
FROM Members

Answer 3

Could you try this ? I didn't test it.
With Member_start_dt as
(
select *, (select start_dt from Pplan where M.start_date <= start_dt AND M.start_date >= end_dt) as Pplan_date
from Members M
),
Member_by_plan as
(
select *, ROW_NUMBER () over (partition by Pplan_date order by start_date) num
from Member_start_dt
)
update M
Set M.start_date = MBP1.start_date
from Members M
inner join Member_by_plan MBP1 ON MBP1.member = M.Member AND num = 1
inner join Member_by_plan MBP2 ON MBP2.member = M.Member AND MBP2.Pplan_date = MBP1.Pplan_date AND MBP2.start_date = M.start_date