sql - Joining tables based on the maximum value -

-

A simplified example of what I'm talking about: 

  table : Examinations of students _____________ ____________________________________ | ID | Name | | ID | Student_id | Score | Date | | ---- + ------ | | ---- + ------------ + ------- + -------- | | 1 | Gym | | 1 | 1 | 73 | 8/1/09 | | 2 | Joe | 2 | 1 | 67 | 9/2/09 | | 3 | Jai | | 3 | 1 | 93 | 1/3/09 | | ____ | ______ | | 4 | 2 | 27 | 4/9/09 | | 5 | 2 | 17 | 8/9/09 | | 6 | 3 | 100 | 1/6/09 | | ____ | ____________ | _______ | ________ |

For this question, suppose at least one exam result has been recorded in each student.

How do you choose each student with them the highest score? Edit : ... and other fields in that record?

Expected Output: 

  _________________________ | Name | Score | Date | | ------ + ------- | -------- | | Gym | 93 | 1/3/09 | | Joe 27 | 4/9/09 | | Jai | 100 | 1/6/09 | | ______ | _______ | ________ |

Welcome to all types of DBMS.

Answering the edited question (i.e. also obtaining related columns).

In SQL Server 2005+, the best way would be to use a combination with this one like this: 

  as exam_data (r.student_id, r. Score, r.date, row_number ()) (r.student_id by division by r.score desc), select exam_results r as sn, s.name, d.score, d.date, d.student_id students To join exam_data d s.id = d.student_id where d.rn = 1;

For ANSI-SQL compliance solutions, a subquery and self-matching will work, such as: 

  select s.name, r.student_id , From r.score, r.date (choose r.student_id, by r.student_id by exam_results r group max_score as max) by joining exam_results at r.student_id = d.student_id and r.score = d. Join Max_score students at s.id = r.student_id;

This final form holds that the student_id / max_core combination is not duplicate, if and / or you want to plan to de-duplicate them, You will need to use to decide which drag to connect with some determinism. For example, suppose that if you want to break a tie based on the most recent maximum score, then the same There may not be many records for a given student with the status, so you do something like: 

  select s.name, r3.student_id, r3.score, r3.date , From r3.other_column_a, ... select (r2.student_id, from max_score as r2.score, max (r2.date) as max_score_max_date (R1.student_id, max (r1.score) from exam_results r1 group R1.student_id as max_score) r2.student_id = d.student_id and r2.score = d.max_score at group r2.student_id, r2 at exam_results r2. Score) r may include exam_results r3 r3 .student_id = r.student_id and r3.score = r.max_score and r3.date = r.max_score_max Join students at _date s.id = r3.student_id;

Edit: Added a proper de-duplication query thanks to the good catch of Mark in the comment


Comments

Post a Comment

Popular posts from this blog

c# - How to capture HTTP packet with SharpPcap -

-
I would like to capture all incoming HTTP packets on my machine. To do this, I am using SharpPcap which is a WinPcap The cover is. SharpPcap works very well, but it captures TCP packets and what it wants to do for me is a very low level. Does anyone know how can I easily get full HTTP requests / reactions from all these TCP packets? Thanks SharpPcap is already able to capture the packet in the same way That's what the virus does (just in the code instead of the GUI). And you can either either parse them directly or you can put them in the drive in the common .pcap file format. The steps to parse the capture are: Open a connection at any time Loop a while Or start capturing using an event callback Parsing the raw packet for the type you want If you are reading .PPP dump files In addition to calling you an offline capture reader is almost the same, there is no need to select an interface, and you can set the majority There is no need to do the modes. All st...
Read more

php - Multiple Select with Explode: only returns the word "Array" -

-
By using Wordpress I have created a multiple selection box so that users can select categories to exclude. When the page is initially loaded, I see my predefined default option. However, when I select a new value and I save ... I only see the word "Array" and have not chosen anything else? & lt; Class = "amultiple" id = "& lt; php echo $ value ['id'] ;? gt;" name = "& gt; php echo $ value ['id'] ;; gt; []" Multiple = "multiple" size = "8" & gt; & Lt ;? Php global option; Foreign currency ($ value as value $) {if (get_settings ($ value ['id']) === FALSE {$$ value ['id'] = $ value ['std']; } And {$$ value ['id'] = get_settings ($ value ['id']); }} $ Ranges = & amp; Amp; Categories ('type = post & orderbiz = name & amp; hide_empty = 1'); If ($ ranges) {$ ex_cat = implode (',', $ tt_cat_exclude); Forex Currency ($ range a...
Read more

php - jQuery AJAX Post not working -

-
I do not understand why this script does not work. It has something to do within AJAX PostScript / Function. Right now, when I submit my form, it runs php code on the same page. What it should do, send the values ​​of the form for Project_Azax.fp, then there will be a refund of success on the page which is correct or false. $ (document) .ready (function () {$ ('div # didIt'). Hide (); $ ('form [name = adminForm]'). Submit (function () ($ {'.post' ('/ project_ajax.php', {action: $ ('[name = action]') Val (), pId: $ ('[name = pId]'). Val (), name ('[Name = name]'. Val (), url: $ ('[url = url]'). Val (), summary: ('[summary = summary]'). Val ()}, Function (data) {if (data.success) {$ ('div # didIt') .Sliddown ('slow');} and {warning ('unsuccessful SA!');}}, 'Jason'); return false ;});}); What is the code for project_ajax.php below ... if ($ _ POST ['action'] == ...
Read more