mysql - Why are variables being cut out? -

-

high school students trying create version of facebook our school. right stuck on joining tables in trial database before can release it.

to join tables post, users, , friends:

users user    name 1       hallie   2       dylan 3       sarina 4       dominic  friends user    friend 1       2 1       3 1       4 2       1 3       1 4       1 2       4 4       2 3       2 2       3  posts | user | postid | post | +------+--------+------+ |    1 |    101 |  tigerbook!          | |    2 |    102 |  pregnant.              | |    1 |    103 |  peeps                | |    4 |    104 |  giant buzz lightyears rock. | |    3 |    105 |  die tucker die              | |    1 |    106 |  murhur de derpity derp      | |    2 |    107 |  banana spaghetti squid      | |    4 |    108 |  chicken                     |

we used code:

select users.user,         users.name,         posts.postid,         posts.post,         tmp.friend    (select friend,                 user            friends          group  friend) tmp         join users           on tmp.user = users.user         join posts           on posts.user = users.user;

and comes result of:

+------+---------+--------+-------------------------+--------+ | user | name    | postid | post                    | friend | +------+---------+--------+-------------------------+--------+ |    1 |  hallie |    101 |  tigerbook!     |      2 | |    1 |  hallie |    101 |  tigerbook!     |      3 | |    1 |  hallie |    101 |  tigerbook!     |      4 | |    2 |  dylan  |    102 |  pregnant.         |      1 | |    1 |  hallie |    103 |  peeps           |      2 | |    1 |  hallie |    103 |  peeps           |      3 | |    1 |  hallie |    103 |  peeps           |      4 | |    1 |  hallie |    106 |  murhur de derpity derp |      2 | |    1 |  hallie |    106 |  murhur de derpity derp |      3 | |    1 |  hallie |    106 |  murhur de derpity derp |      4 | |    2 |  dylan  |    107 |  banana spaghetti squid |      1 | +------+---------+--------+-------------------------+--------+

it cuts out posts 104, 105, , 108. posted users 3 , 4. , ignores fact user 2 friends 3 , 4, 1 shows.

why not bringing users 3 , 4? should try different code?

look subquery returns:

| friend | user | ----------------- |      1 |    2 | |      2 |    1 | |      3 |    1 | |      4 |    1 |

because of group by, lose multiple user values associated friends.

why did use subquery instead of joining friends table itself?

select users.user,    users.name,    posts.postid,    posts.post,    friends.friend friends    join users      on friends.user = users.user    join posts      on posts.user = users.user; 
| user |    name | postid |                        post | friend | ------------------------------------------------------------------ |    1 |  hallie |    101 |          tigerbook! |      2 | |    1 |  hallie |    103 |                peeps |      2 | |    1 |  hallie |    106 |      murhur de derpity derp |      2 | |    1 |  hallie |    101 |          tigerbook! |      3 | |    1 |  hallie |    103 |                peeps |      3 | |    1 |  hallie |    106 |      murhur de derpity derp |      3 | |    1 |  hallie |    101 |          tigerbook! |      4 | |    1 |  hallie |    103 |                peeps |      4 | |    1 |  hallie |    106 |      murhur de derpity derp |      4 | |    2 |   dylan |    102 |              pregnant. |      1 | |    2 |   dylan |    107 |      banana spaghetti squid |      1 | |    2 |   dylan |    102 |              pregnant. |      3 | |    2 |   dylan |    107 |      banana spaghetti squid |      3 | |    2 |   dylan |    102 |              pregnant. |      4 | |    2 |   dylan |    107 |      banana spaghetti squid |      4 | |    3 |  sarina |    105 |              die tucker die |      1 | |    3 |  sarina |    105 |              die tucker die |      2 | |    4 | dominic |    104 | giant buzz lightyears rock. |      1 | |    4 | dominic |    108 |                     chicken |      1 | |    4 | dominic |    104 | giant buzz lightyears rock. |      2 | |    4 | dominic |    108 |                     chicken |      2 |

http://sqlfiddle.com/#!2/27eb3d/6


Popular posts from this blog

How to calculate SNR of signals in MATLAB? -

-
i've encountered simple, yet fundamental problem on calculating snr: there several signals : s1 = original , pure clean signal without noise. n1 = white gaussian noise going added s1. s2 = s1 + n1 (the noisy signal before performing noise-reduction algorithm) s3 = noise-reduced signal (after performing noise reduction algorithm) n2 = s3 - s1 (the amount of noise after performing noise-reduction algorithm) now want compare snr before , after performing noise-reduction algorithm. which signals should consider snr_before!? s1/n1 or s2/n1 ? which signals should consider snr_after!? s3/n1 or s3/n2 ? which commands or functions should use in matlab in order compute snr_before , snr_after? thanks billion putting time on helping me. what know calculating snr before : snrbeforenoise = mean( signal .^ 2 ) / mean( noise .^ 2 ); and snr after : residual_noise = signal - noise_reduced_signal; snr_after = mean( signal .^ 2 ) / mean( residual_noise .^ 2
Read more

c# - Attempting to upload to FTP: System.Net.WebException: System error -

-
i have api takes in xml , uploads files based on information in xml. uploads on schedule (also xml), , have tested surrounding , know works. i getting error 40% of time on first file attempt upload in each time cycle (time cycle = 45 minutes files, 30 minutes others). here code upload: try { loggerftp.log("uploading file: " + filename, false); // create request. ftpwebrequest request = (ftpwebrequest)webrequest.create(appsettingsftp.ftpurl + @"/" + filename); request.method = webrequestmethods.ftp.uploadfile; request.timeout = 6000000; //set 100 minutes //request.timeout = -1; //set infinite // add login credentials. request.credentials = new networkcredential(appsettingsftp.ftplogin, appsettingsftp.ftppassword); // grab file contents. streamreader sourcestream = new streamreader(appsettingsftp.uploadfiledirectory + filename); byte[] filecontents = encoding.utf8.getbytes(sourcestream.readtoend()); sourcest
Read more

ios - UISlider customization: how to properly add shadow to custom knob image -

-
Image
i need place custom knob image shadow uislider. far have image of 38x38, of there region defines shadow of knob. now while using image, when slide knob extreme ends actual knob not able cover end points, hence end points visible under transparent region of knob image this code using customize uislider uiimage *slidebtimg = [uiimage imagenamed:sliderknobimg]; [self.ratingslider setthumbimage:slidebtimg forstate:uicontrolstatenormal]; [self.ratingslider setthumbimage:slidebtimg forstate:uicontrolstatehighlighted]; how can implement custom knob shadow beneath it, covering end points?? look inside uislider.h , there methods let customize slider knob , track needed. (ios 2.0 , above) // lets subclass lay out track , thumb needed - (cgrect)minimumvalueimagerectforbounds:(cgrect)bounds; - (cgrect)maximumvalueimagerectforbounds:(cgrect)bounds; - (cgrect)trackrectforbounds:(cgrect)bounds; - (cgrect)thumbrectforbounds:(cgrect)bounds trackrect:(cgrect)rect value:
Read more