php - Most efficient way to get the data from database -

so have pretty simple. have 1 table

categoriemain

like

catmainid

catmainname

and 1 table:

categoriesub

like

catid

catname

catmainid

'

what want :

a list catmainname's , under names catsubnames.

catmainid1

all catsubnames catmainid1

catmainid2

all catsubnames catmainid2

etc etc

currently use php data like

 select * categoriemain 

and in while loop do

 select * categoriesub catmain id = $row['catmainid'] 

but inefficient because if have 10 catmainid's 10 query's (for each 1 while)

what efficient way list this, thinking putting in arrays or couldn't working?

select * categoriemain join categoriesub on categoriemain.catmainid=categoriesub.catmainid order categoriemain.catmainid