MySQL: How to fetch all columns with distinct clause on one column with latest created record -


i have db table structure

id, latitude, longitude, altitude, deviceid, createddate

i trying create query fetches distinct deviceid has been created @ latest..

i have tried query

select distinct deviceid `deviceposition` order createddate desc

based on beiller's post, try solution:

select deviceid, createddate  `deviceposition` outer_dev_pos  createddate = (     select max(inner_dev_pos.createddate)     `deviceposition` inner_dev_pos     inner_dev_pos.deviceid = outer_dev_pos.deviceid )  order createddate desc;

update: explanation:

we accessing same table 2 times in query, once in outer select , once in subselect (the inner select). therefor, necessary tell in query access' deviceid , createddata mean. important in clause of subselect:

where inner_dev_pos.deviceid = outer_dev_pos.deviceid

if didn't use alias names inner_dev_pos , outer_dev_pos 2 accesses of same table, line read:

where deviceid = deviceid

which not make sense.


Comments

Post a Comment

Popular posts from this blog

c# - Send Image in Json : 400 Bad request -

from android trying send image class of data, iis webservice. (c#) the problem 400 bad request . the image being encoded base64 . , placed json rest of class elements. my guess base64 not valid inside json. server not understand it. if set string "" , post accepted fine. so question is, how make base64 valid within json array? ( tried url.encode no success). or how should send image android webservice? gson gson = new gson(); string json = gson.tojson(record); // record has param { string base64photo } how big image? i'm pretty sure surpassing iis json size limit (default 4 mb). check http://geekswithblogs.net/frankw/archive/2008/08/05/how-to-configure-maxjsonlength-in-asp.net-ajax-applications.aspx or http://www.webtrenches.com/post.cfm/iis7-file-upload-size-limits good luck!
Read more

javascript - addthis share facebook and google+ url -

i attempting use addthis create simple url shares whichever current page user on when click share button. of right now, have twitter working. when user clicks, able see url populated in tweet box. when user clicks facebook or google+, url doesn't seem show in share box. <ul class="addthis_toolbox addthis_default_style "> <li><a class="addthis_button_facebook"><img src="/img/facebook-social.png" width="20" height="20" border="0" alt="share" /></a></li> <li><a class="addthis_button_twitter"><img src="/img/twitter-social.png" width="20" height="20" border="0" alt="share" /></a></li> <li><a class="addthis_button_google_plusone_share"><img src="/img/google-social.png" width="20" height="20" border="0" alt="s...
Read more

ios - Show keyboard with UITextField in the input accessory view -

i have buttona , when buttona clicked, want keyboard show uitextfield in inputaccessoryview. there way have keyboard show manually , set inputaccessoryview without having uitextfield initially? thanks. you cannot summon keyboard without object can become first responder. there 2 ways work around: subclass uiview , implement uikeyinput protocol in it. example: in .h file: @interface inputobject : uiview<uikeyinput> @property (nonatomic, copy) nsstring *text; @property (nonatomic, strong) uiview *inputaccessoryview; // must override inputaccessoryview , since it's readonly default @end in .m file, implement protocol: - (bool)canbecomefirstresponder { return yes; } - (bool)hastext { return [self.text length]; } - (void)inserttext:(nsstring *)text { nsstring *selftext = self.text ? self.text : @""; self.text = [selftext stringbyappendingstring:text]; [[nsnotificationcenter defaultcenter] postnotificationname:kinputobjec...
Read more