mysql - SQL Insert into and Select multiple columns? -

so have tables this:

communication: (calls made)

timestamp            fromidnumber toidnumber generallocation  2012-03-02 09:02:30  878          674        grasslands  2012-03-02 11:30:01  456          213        tundra  2012-03-02 07:02:12  789          654        mountains 2012-03-02 08:06:08  458          789        tundra  

and want create new table has distinct fromidnumber , toidnumber's.

this sql fiddle it.

this works:

insert commidtemp (`id`) select distinct communication.fromidnumber communication union distinct  select distinct communication.toidnumber communication; 

and got:

 id    878  456  789  674  213  654  365 

but wonder if there more efficient way, because dataset have has millions , millions of lines , didn't know performance of union distinct.

i tried

insert commidtemp (`id`)  select distinct communication.fromidnumber , communication.toidnumber  communication;  

but didn't work... there other way more efficiently? i'm pretty new sql, appreciated, thank you!!

first thing: not have experience big tables. have test out following tipps find out if working in situation:

1. create index in source table

make sure both columns fromidnumber , toidnumber have index, i.e.

alter table communication add index (fromidnumber); alter table communication add index (toidnumber); 

2. try remove distinct

i not find faster query example, though might try query without distinct keyword - using union returns distinct values definition. sql gives same result current query:

insert commidtemp (`id`) select fromidnumber communication union  select toidnumberfrom communication; 

3. use primary key in temp table

also try approach setting commidtemp.id column primary key , use insert ignore - useful if want update table without deleting contents:

create table commidtemp (id int primary key);  insert ignore commidtemp (`id`) select fromidnumber communication union select toidnumber communication;