Produces a data.frame that describes the output of a query. The data.frame should have as many rows as there are output fields in the result set, and each column in the data.frame describes an aspect of the result set field (field name, type, etc.)
This documentation page describes the generics. Refer to the documentation pages linked below for the documentation for the methods that are implemented in various backend packages.
An object inheriting from DBIResult.
Other arguments passed on to methods.
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.
This section gives a complete overview over the flow for the execution of queries that return tabular data.
Most of this flow, except calling
is implemented by
dbGetQuery(), which should be sufficient
unless you want to access the results in a paged way
or you have a parameterized query.
This flow requires an active connection established by
vignette("dbi-advanced") for a walkthrough.
Optionally, bind query parameters with
This is required only if the query contains placeholders
$1, depending on the database backend.
dbColumnInfo() to retrieve the structure of the result set
without retrieving actual data.
dbFetch() to get the entire result set, a page of results,
or the remaining rows.
Fetching zero rows is also possible to retrieeve the structure of the result set
as a data frame.
This step can be called multiple times.
Only forward paging is supported, you need to cache previous pages
if you need to navigate backwards.
dbHasCompleted() to tell when you're done.
This method returns
TRUE if no more rows are available for fetching.
dbClearResult() to clean up the result set object.
This step is mandatory even if no rows have been fetched
or if an error has occured during the processing.
It is good practice to use
to ensure that this step is always executed.
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.
Column names that correspond to SQL or R keywords are left unchanged.