But how do you find
Using multiple queries and a program, there are many ways to perform this type of data retrieval - but I want to do this with a single query.
This is one of those areas where different databases implement the function in different ways.
Simple "group by"
select "Name", max("Date_Time") from "Programs_tbl" group by "Name"But it can not be directly extended to include other fields.
Let the "where" Clause Contain a Second Query
select * from "Programs_tbl" xx where xx."Date_Time" = (select max("Date_Time") from "Programs_tbl" yy where xx."Name" = yy."Name")Notice that because the same table is used in both queries, the 2 result sets must be assigned aliases - xx and yy in this example.
Place the Second Query in a "Join"
SELECT rh.user_name, rh.report_name, rh.report_run_date FROM report_history rh, (SELECT max(report_run_date) as maxdate, report_name FROM report_history GROUP BY report_name) maxresults WHERE rh.report_name = maxresults.report_name AND rh.report_run_date = maxresults.maxdate;According to Introduction to PostgreSQL SQL - Nested subqueries and derived tables, this imbedded query is known as either a derived table or a temporary view.