Consider a table and a query referring to only a subset of the columns
in that table. How early in the query evaluation is the projection
carried out?
Are the columns to be selected filtered out as early as in the very
access method that reads the table rows from the buffer, or are the
projection handled later, after the whole row has been fetched by the
access method?
Does it depend on the complexity of the query, how far down the three
that the projection is handled out?
Thanks!