How to Find the Most Recent Position for Each Security Using SQL?

Groupwise Maximum

Problem:

Obtain the latest position for each security from the following table:

id	security	buy_date
26	PCS	2012-02-08
27	PCS	2013-01-19
28	RDN	2012-04-17
29	RDN	2012-05-19
30	RDN	2012-08-18
31	RDN	2012-09-19
32	HK	2012-09-25
33	HK	2012-11-13
34	HK	2013-01-19
35	SGI	2013-01-17
36	SGI	2013-02-16
	KERX	2013-02-20
	KERX	0000-00-00

Solution:

The following query retrieves the maximum buy date for each security, along with the corresponding ID:

SELECT p1.id, 
       p1.security, 
       p1.buy_date 
       FROM positions p1
left join
            positions p2
                on p1.security = p2.security
                   and p1.buy_date < p2.buy_date
      where 
      p2.id is null;

This query efficiently finds the latest position for each security using a left join. It compares the buy dates of each security and only selects rows where no later buy date exists. This optimized solution ensures accurate results in a faster execution time compared to subquery-based approaches.

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