mysql - Select items that doesn't have a specific value in another table -


i trying select items doesn't have specific value in table, able achieve result wanted using subquery, it's slow wondering if differently...

select     content.*,     (select views      content_views      content_views.content = content.record_num     ) views content right join watch_log on content.record_num = watch_log.content content.enabled = 1     , 24 not in         (select niche          content_niches          content_niches.content = content.record_num         ) order content.encoded_date desc limit 0,6

i tried using left outer join, couldn't same result...

select     content.*,     (select content_views.views      content_views      content_views.content = content.record_num     ) views content right join watch_log on content.record_num = watch_log.content left outer join content_niches on content.record_num = content_niches.content , content_niches.niche = 24 content.enabled = 1 order content.encoded_date desc limit 0,6

mixing left , right outer joins confusing. in fact, right join isn't needed. can replaced left join. in case, can replaced inner join, because where clause turns inner join. so, how about:

select c.*,        (select views         content_views cv         cv.content =  c.record_num        ) views content c join      watch_log wl      on c.record_num = wl.content c.enabled = 1 ,       not exists (select 1                   content_niches cn                   cn.content = c.record_num ,                         cn.niche = 24                  ) order c.encoded_date desc limit 0, 6;

for performance want indexes: content(enabled, encoded_date, record_num), content_views(content, views), , content_niches(content, niche).

notes:

  • don't mix different types of outer joins, unless really, understand doing.
  • use table aliases abbreviations of table names. makes queries easier write , read.
  • whatever preference formatting, don't start line in query desc (or asc); modifier on order by.
  • not exists better not in. former handles null values way expect. latter returns nothing if there null values.

Comments

Post a Comment

Popular posts from this blog

javascript - jQuery: Add class depending on URL in the best way -

i have html progress meter: <div class="col-md-3" style="margin-left: -20px;"> <div class="progress-pos active" id="progess-1"> <div class="progress-pos-inner"> login </div> </div> </div> <div class="col-md-3 progress-pos-container"> <div class="progress-pos" id="progess-2"> <div class="progress-pos-inner"> scan items </div> </div> </div> <div class="col-md-3 progress-pos-container"> <div class="progress-pos" id="progess-3"> <div class="progress-pos-inner"> confirm address </div> </div> </div> <div class="col-md-3 progress-pos-container"> <div class="progress-pos" id="progess-4"> <div class="progress-pos-in...
Read more

caching - How to check if a url path exists in the service worker cache -

i need check if particular url path exists in service worker cache. example, suppose url is: /myserviceworker/service?a=110&b=70 this url exists in cache, there many of them different values of , b. now, suppose want refresh of these urls, how can that? i want know how access key values service worker cache. if know key, plan follows: var url = new url(key); if(url.pathname === "\/myserviceworker/service") refetch key but not sure how cache key , in format is. mean, string or url? cache api has match() method returns promise resolving in response object if match or undefined if no match exists. second parameter object can specify ignoresearch not take account url parameters. the ignoresearch option supported firefox ( chrome status here ). in other hand, retrieve cache entries, can use keys() method.
Read more

Redirect to a HTTPS version using .htaccess -

i need modify .htaccess file redirect urls https version without "www". http://example.com --> https://example.com http://www.example.com --> https://example.com https://www.example.com --> https://example.com this how .htaccess file looks like: rewriteengine on rewritecond %{request_filename} !-d rewritecond %{request_filename} !-f rewriterule ^(.*)$ redirect.php?id=$1&page=$2 [qsa,l] what modifications need make .htaccess in order forward https without "www"? it depends on doing current code. looks file called redirect trying display php page seo friendly url. think might confusing people. anyway, need , force https without www, need 1 more rule above. also second rule needs two capture groups in rewriterule test string because wanting 2 different values using $1 , $2 references. rewriteengine on #rediect www non www and/or http https --- combinations. rewritecond %{http_host} !^example\.com [nc,or] rewritecond %{https} !^...
Read more