returns a data frame
with at least two columns
"type" (in that order)
(and optional columns that start with a dot).
"type" columns contain the names and types
of the R columns of the data frame that is returned from
"type" column is of type
character and only for information.
Do not compute on the
"type" column, instead use
dbFetch(res, n = 0)
to create a zero-row data frame initialized with the correct data types.
An attempt to query columns for a closed result set raises an error.
A column named
row_names is treated like any other column.
The column names are always consistent
with the data returned by
If the query returns unnamed columns,
non-empty and non-
NA names are assigned.
In the case of a duplicate column name, the first occurrence
retains the original name, and unique names are assigned for
the other occurrences.
Column names that correspond to SQL or R keywords are left unchanged.