database - MySQL Relationships & Joins -


in mysql database there relationships between tables , primary key of 1 table stored foreign key in second table, there still need perform join?

if there is, point on declaring relationship? i'd take stab in dark , it's indexing or related tables can find related records faster? i've tried googleing this, can't seem find much. i'm sure there loads out there on this, don't know keywords search for.

here example of table 1 , table 2: 

------------------- table 1 ---------------------- create table if not exists `db_hint`.`user` ( `id` int unsigned not null auto_increment, `fb_id` int not null, `last_logged_in` datetime null, `permissions` int unsigned not null, primary key (`id`), index `permissions_id_idx` (`permissions` asc), constraint `permissions_id` foreign key (`permissions`) references `db_hint`.`permissions` (`id`) on delete no action on update no action) engine = innodb;  ----------------- table 2 ---------------------- create table if not exists `db_hint`.`user_stat` ( `id` int unsigned not null auto_increment, `user_id` int unsigned not null, primary key (`id`), index `user_id_idx3` (`user_id` asc), constraint `user_id` foreign key (`user_id`) references `db_hint`.`user` (`id`) on delete no action on update no action) engine = innodb;

when performing kind of join, innodb engine use relationship in way? thanks.

the point of declaring foreign key enforce data consistency. still need join in order desired data. in mysql foreign keys improve performance, don't expect comparable indexes.


Comments

Post a Comment

Popular posts from this blog

c++ - Difference between pre and post decrement in recursive function argument -

i have following sample code used pre-decrement void function(int c) { if(c == 0) { return; } else { cout << "dp" << c << endl; function(--c); cout << c << endl; return; } } this function give output input 4 : dp3 dp2 dp1 dp0 0 1 2 3 but when use post decrement void function(int c) { if(c == 0) { return; } else { cout << "dp" << c << endl; function(c--); cout << c << endl; return; } } output goes in infinite loop dp4 can explain me in detail why happens ? this happens because function(c--) called same value of c , when finishes c decremented. recursively called, hence called same value no chance of return , hit stack overflow error. assume this, int x = 1, y = 0; y = x++ result y == 1 , x == 2. if y = ++x , bot x , y 2.
Read more

php - Nothing but 'run(); ' when browsing to my local project, how do I fix this? -

i added new project. made mistake in projectname.conf file in sites-available apache2, led me reinstalling apache2. after reinstalling , re-enabling projects on every page of every project .. <body> run(); </body> .. i've run composer update, restarted service, restarted pc, checked config files, tried disabling new project. there nothing in error log, , access.log: 127.0.0.1 - - [15/may/2015:01:40:47 +0200] "get / http/1.1" 304 181 "-" "mozilla/5.0 (x11; ubuntu; linux x86_64; rv:38.0) gecko/20100101 firefox/38.0" maybe i'm forgetting apache2 reinstall? don't think did different last time installed it. looks haven't setup php correctly. take @ this great guide , maybe you're forgetting link php config apache2.
Read more

php - How can I echo out this array? -

i don't know how go grabbing data in variable , put foreach loop. class tree{ private $info = array( array('name'=>'jim','state'=>'nu','company'=>'nu','phone'=>array('cell'=>'5615111111','office'=>'5611111111'),'email'=>array('primary'=>'exs@example.com','ex@there.com')), array('name'=>'joe smith','city'=>'phoenix','phone'=>'4805551111','email'=>'jsmith@some_email.com'), array('name'=>'john doe','city'=>'chandler','company'=>'doe co.','email'=>array('jdoe@gmail.com','personal'=>'email@email.com'),'phone'=>'6025550002') ); } if you're inside of class, can access private variable using $this->variablename . example, i...
Read more