Actually, one alternative approach would be: use a search index to autocomplete after even a basic 'SELECT' statement (no other context), but then fill the FROM clause based on the selection.

i.e. - type:

'select city'

prompts with:

'city (table airports)'

'city (table populations)'

'city (table companies)'

And then, upon selection, you have a statement: 'select city from <selected-table>'.

There's a lot more here though. Worth pondering for a while I think.