How do I select random rows in MySQL? -

- 

mytable  pid name field === ==== ===== 1    a1   0 2    a2   1 3    a3   1 4    a4   0    5    a5   0

this table structure. here want select randomly 4 rows use rand() mysql function in query questions

how pair rows. mean, wanna select pid 2 , 3 1 ofter another. need in bellow order. i don't want break pair a2 a3

a1 a2 a3 a4 or a2 a3 a4 a1 or a2 a3 a4 a5 or a4 a5 a2 a3 , etc

i used query below it's not working me 

select * mytable order rand() asc limit 0,4

turbod close answer, ordering randomly, when seems wanted order pid, after getting random rows wanted in conjunction ones concerning a2 , a3:

(     select *     `mytable`              name ='a2' or          name ='a3'     limit 2 ) union (     select distinct *     `mytable`              name !='a2' or          name !='a3'     order rand( ) limit 2 )  order `pid`

Comments

Post a Comment

Popular posts from this blog

Javascript line number mapping -

-
magically formatted comments change reported line number of javascript errors in browsers; this: //@line n "f" n line number , f file name. unfortunately, //@line appears ungoogleable. know there documentation on feature, , browsers support it? (i found references here , here .) from can find available in mozilla based browsers. it using js_setoptions command can turn these options on or off depending on values passed. https://developer.mozilla.org/en/js_setoptions
Read more

c# - Is it possible to remove an existing registration from Autofac container builder? -

-
something along lines: builder.registertype<mytype>().as<itype>(); builder.registertype<mytype2>().as<itype>(); builder.deregistertype<mytype>().as<itype>() var container = builder.build(); var types = container.resolve<ienumerable<itype>>(); assert.istrue(types.count == 1); assert.istrue(types[0].gettype == typeof(mytype2)); scenario: go through bunch of assemblies , go register types want make sure have 1 implementation of given type. need before create container. track on own nice if autofac me bit. this cannot done directly using containerbuilder , unless start on new one. mind you, having first built container should able construct new container filtering away unwanted types , reusing registrations first container. this: ... var container = builder.build(); builder = new containerbuilder(); var components = container.componentregistry.registrations .where(cr => cr.activator.limittype != typ...
Read more

php - Mysql PK and FK char(36) vs int(10) -

-
i have read mysql can handle indexes , searches better if tables keys integers rather char(36) uuid's. is worth converting int(10)? note: use 1 server , have have plans use multiple databases concurrently therefore removing 1 of big reasons using uuid. our tables innodb if makes difference. thanks in advance. usually rdbms can handle integer keys pk more efficient, other datatypes. reason how build index column, yes: long dont require string (or other typed) keys, should use integers. however: char(36) , int(10) far away being equal, because int(10) much smaller, char(36). dont know, if require many different keys, should keep in mind. update, complete last paragraph: int(10) 32-bit, char(36) 36 - ^byte^ (= 288-bit). not mean, int consumes less space, means, char(36) has 4 times more different keys.
Read more