They work on any join that is able to make use of them. If you
preface the select statement with explain query plan then it will give
you some info, e.g.
> sqldf('explain query plan select * from main.A natural join main.B')
order from detail
1 00 TABLE
Thank you very much for these clarifying responses, Gabor.
I had mistakenly assumed that creating the index on Tid restricted the
natural join to joining on Tid. Can you describe when and how indices speed
up joins, or can you point me to resources that address this? Is it only for
natural joins o
Although that works I had meant to write:
> names(B)[2] <- "dfNameB"
> # ... other commands
> sqldf('select * from main.A natural join main.B')
so that now only Tid is in common so the natural join just picks it up
and also the heuristic works again since we no longer retrieve
duplicate column na
There are two problems:
1. A natural join will join all columns with the same names in the two
tables and that includes not only Tid but also dfName and since there
are no rows that have the same Tid and dfName the result has zero
rows.
2. the heuristic it uses fails when you retrieve the same co
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