SQL exclude duplicated pairs of columns from a two-column select -


i don't know how describe problem , haven't found answer. have 2 tables, rating , reviewer. want every pair of reviewers names if rated same movie. have sql query:

select distinct re1.name, re2.name  reviewer re1, reviewer re2, rating ra1, rating ra2 re1.rid=ra1.rid , re2.rid=ra2.rid , ra1.mid=ra2.mid , re1.rid!=re2.rid;

this tables structure: rating (rid, mid, stars, ratingdate), reviewer(rid, name)

this want get:

name                       name               daniel lewis               elizabeth thomas  elizabeth thomas           james cameron  ashley white               chris jackson mike anderson              sarah martinez brittany harris            chris jackson

this get:

name                           name                          ------------------------------ ------------------------------ daniel lewis                   elizabeth thomas                elizabeth thomas               james cameron                   chris jackson                  brittany harris                 chris jackson                  ashley white                    ashley white                   chris jackson                   james cameron                  elizabeth thomas                mike anderson                  sarah martinez                  sarah martinez                 mike anderson                   elizabeth thomas               daniel lewis                    brittany harris                chris jackson

how remove duplicate rows name1 , name2 have been selected name2, name1 ? hope clear enough. thanks.

its subtle change (> vs !=), want use diagonal elimination approach, whereby exclude reviewer rid lower current one:

select distinct re1.name, re2.name  reviewer re1   inner join rating ra1     on re1.rid=ra1.rid cross join   reviewer re2   inner join rating ra2     on re2.rid=ra2.rid ra1.mid=ra2.mid ,  re1.rid > re2.rid;

this way, don't 'double count' pairs of reviewers have match on opposite / symmetric side of diagonal.

i've taken liberty of moving join conditions joins, rather in where clause.

sqlfiddle here


Comments

Post a Comment

Popular posts from this blog

asp.net mvc - SSO between MVCForum and Umbraco7 -

i need integrate sso between mvcforum (forum of company) , umbraco7 (manages cms company). however struggling shared authentication work. tried several ways suggested on other threads still not running expected. here did: 1. in mvcforum (forum.mywebsite.com) 1.1. machine key in web.xml: <machinekey validationkey="the same key umbraco7" decryptionkey="the same key umbraco7" validation="sha1" decryption="aes" /> 1.2. authenticate forms in web.xml <forms name="my-sso-auth" protection="all" path="/" timeout="43200" domain="forum.mywebsite.com" loginurl="/members/logon" enablecrossappredirects="true" /> 2. in umbraco7 (news.mywebsite.com) 2.1. machine key in web.xml: <machinekey validationkey="the same key mvcforum" decryptionkey="the same key mvcforum" validation="sha1" decryption="aes" /> 2.2. a
Read more

Python Tkinter keyboard using bind -

i have problem using bind option can click button in keyboard, , call function once key pressed. tried taking other codes have similar purpose , saw i'm doing pretty same, though still have problem must've missed. thankful if me this. here's code: # -*- coding: utf-8 -*- #imports tkinter import * pil import imagetk, image import time import tkmessagebox #===========================================================================================================================================# #tkinter class class app(frame): def __init__(self, master=none): frame.__init__(self, master) self.pack() #===========================================================================================================================================# #game pieces classes class board: def __init__(self, rows = 7, columns = 6, picture_height = none, picture_width = none): self.rows = rows self.columns = columns self.picture
Read more

ubuntu - Selenium Node Not Connecting to Hub, Not Opening Port -

i'm trying set demo selenium grid. have digital ocean ubuntu 14.02 droplet. (i have 2 , tried set using 2 different machines got nowhere.) i'm trying run hub , node both locally. here input both hub, node, , nmap results. https://gist.github.com/mekhami/d5bbecca5ff0de9d2dc9 so, node starting tcp connection reset , port it's supposed operate on closed. i have had no luck in number of different options , configurations work. but... of course, worked randomly once. don't know why, don't know did, know 1 brief moment, node connected , saw on grid console. tried run test , went down again , i've never seen come up. please let me know more information can provide. update: randomly came online again. don't know happened, might related timeout or time_wait or going on. this because vm/server not have enough entropy available. to resolve problem, install haveged (or other similar things). the instructions of how install haveged on ubu
Read more