Select records based on last date

In PostgreSQL, to get unique rows for a defined set of columns, the preferable technique is generally DISTINCT ON:

SELECT DISTINCT ON ("ID") *FROM   "Course"ORDER  BY "ID", "Course Date" DESC NULLS LAST, "Course Name";

^{Assuming you actually use those unfortunate upper case identifiers with spaces.}

You get exactly one row per ID this way - the one with the latest known "Course Date" and the first "Course Name" (according to sort order) in case of ties on the date.

You can drop NULLS LAST if your column is defined NOT NULL.

To get unique rows per ("ID", "Course Name"):

SELECT DISTINCT ON ("ID", "Course Name") *FROM   "Course"ORDER  BY "ID", "Course Name", "Course Date" DESC NULLS LAST;

Details in this related answer:

• Select first row in each GROUP BY group?

SELECT "ID", "Course Name", MAX("Course Date") FROM "Course" GROUP BY "ID", "Course Name"

SELECT *FROM (SELECT ID, CourseName, CourseDate,       MAX(CourseDate) OVER (PARTITION BY COURSENAME) as MaxCourseDateFROM Course) xWHERE CourseDate = MaxCourseDate

Here the MAX() OVER(PARTITION BY) allows you to find the highest CourseDate for each Course (the partition) in a derived table. Then you can just select for the rows where the CourseDate is equal to the maximum Coursedate found for that Course.

This approach has the benefit of not using a GROUP BY clause, which would restrict which columns you could return since any non-aggregrate column in the SELECT clause would also have to be in the GROUP BY clause.