Optimize SQL queries

Much needed fix for me.

My commands were taking at least 15 minutes to run after enabling LinkIt

This speeds things up dramatically for me. I think Xurizaemon is probably right in that there are still improvements to be made as I'm also seeing delays introduced into unrelated specific migrations but I don't think the prospect of further optimisations should hold this back from being merged as the improvement is huge.

#8 works for me