>* JOIN
>SELECT cr.plot_id ;
> FROM crzplots cr ;
> JOIN imsfilter ff ON ff.linkfield = cr.plot_id ;
> INTO CURSOR cPlots
>
>* Correlated subquery
>SELECT plot_id ;
> FROM crzplots ;
> WHERE EXISTS (SELECT * FROM imsfilter ff WHERE ff.linkfield = cr.plot_id) ;
> INTO CURSOR cPlots

I think I got it.

Both SQL display the same SYS(3054) message:
Rushmore optimization level for table cr: none
Rushmore optimization level for table ff: none
Joining table ff and table cr using index tag Linkfield

But with about 1.2 million records in crzplots and about 69k in imsfilter, the selection time for the "JOIN" solution is down to .4 seconds.

Should I be concerned that the optimization levels are none? Or can it be even better?