>I am using vfp 6.0
>insert mytable(companyname) select companyname from test_tables
>
>the above command cannot run. Please help

You cannot run correlated queries like that in such an old version. Maybe the easiest would be to get the data and then append or you could run a loop to insert if you wanted to massage the data beforehand.

select companyname from test_tables into cursor temp
select 0
use mytable
append from temp