sql - How do I group by using an average? -

i need display names of business has average quantity of less or equal 300.

table s:

busname     busnum  -------   ---------   bob        a1       lee        a2         ashley     a3   

table sp:

busnum     qty  -------   --------- a1         300     a1         400      a1         100  a2         100 a2         100 a2         200 a3         400 a3         300 

this i'm trying:

select s.busname s s join sp p on p.busnum = s.busnum group s.busname having avg(p.qty) <= 300; 

select busnum , average of qty table sp temporary table, normal join! can do:

select s.busname s, (select busnum, avg(qty) average          sp          group busnum) temporal s.busnum = temporal.busnum , temporal.average <= 300;