This method shouldn't be called be users - it should only be used by
backend implementors who are creating backends that extend the basic
sql behaviour.
Usage
tbl_sql(subclass, src, from, ..., vars = NULL)
Arguments
subclass
name of subclass
...
needed for agreement with generic. Not otherwise used.
vars
If known, the names of the variables in the tbl. This is
relatively expensive to determine automatically, so is cached throughout
dplyr. However, you should usually be able to leave this blank and it
will be determined from the context.