inner join - Mysql query where not exists -

-

i have 3 different tables - subscribers, unsubscribers, mass subscribers.

i'd print out each email mass subscribers table. email can printed if doesn't exist in both subscribers , unsubscribers tables.

i know how arrays, want plain mysql query.

what mysql query be?

thanks!

you can subquery (this slow! please read below line):

select email  subscribers  email not in(select email unsubscribers)

however, bad performance. suggest change way have database, 1 table subscribers, , add column active(tinyint). when unsubscribes, set value 1 0. after can stay in 1 table:

select email subscribers active=1

this faster because of reasons:

  • no subquery
  • the bad, because going select heap of data, , compare strings
  • selecting on integer in fast (especially when index it)

apart fact faster, better database structure. dont want 2 tables doing same, emailadresses. create duplicate data , chance misalignments


Comments

Post a Comment

Popular posts from this blog

jQuery Mobile app not scrolling in Firefox -

-
i have mobile app built in jquery mobile. scrolling fine in chrome & safari, fails scroll in firefox on desktop. have other instances of same app, different features, , works across browsers. life of me, cannot figure this, please help! located here: http://re-brand.us/dsus/index.html seems bug in firefox: bug log . able scroll using keyboard not trackpad on mac. are using mac? i'll keep looking see if can find way around it.
Read more

c++ - How to add Crypto++ library to Qt project -

-
Image
i downloaded crypto++ source , compiled cryptlib project in visual studio 2013, , added generated .lib file qt project, made .pro file this: qt += core gui qt += sql greaterthan(qt_major_version, 4):qt += widgets target = untitled template = app sources += main.cpp\ mainwindow.cpp headers += mainwindow.h \ databasecontrol.h \ test.h forms += mainwindow.ui win32:config(release, debug|release): libs += -l$$pwd/ -lcryptlib else:win32:config(debug, debug|release): libs += -l$$pwd/ -lcryptlibd else:unix: libs += -l$$pwd/ -lcryptlib includepath += $$pwd/ dependpath += $$pwd/ win32-g++:config(release, debug|release): pre_targetdeps += $$pwd/libcryptlib.a else:win32-g++:config(debug, debug|release): pre_targetdeps += $$pwd/libcryptlibd.a else:win32:!win32-g++:config(release, debug|release): pre_targetdeps += $$pwd/cryptlib.lib else:win32:!win32-g++:config(debug, debug|release): pre_targetdeps += $$pwd/cryptlibd.lib else:unix: pre_targetdeps += $$pw
Read more

php array slice every 2th rule -

-
i have array on php outputs in txt file: printing grid -- 1 values -- undef = -9.99e+08 20.2 \nprinting grid -- 1 values -- undef = -9.99e+08 102.0 \nprinting grid -- 1 values -- undef = -9.99e+08 55.1 \nprinting grid -- 1 values -- undef = -9.99e+08 -18.3 \n what point, need nummeric values @ beginning of each rule. 20.2, 102.0, 55.1, -18,3 etc... example, there can more or less in txt file. now do? have tested array slice function can't exclude rule: printing grid -- 1 values -- undef = -9.99e+08 this array slice code... $arraygood = array_slice($arraybad, 1, 4); and foreach loop create text file: $file = fopen("array.txt","w"); foreach ($arraygood $meting => $waarde) { echo fwrite($file,$waarde . '\n'); } fclose($file); thanks! as posted in comments, understanding have array of strings similar following: $lines = array( "printing grid -- 1 values -- undef = -9.99e+08", "20.2 \nprinting grid --
Read more