Information about result typesSource:
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 as data frames.
Most of this flow, except repeated calling of
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 that you want to reuse.
This flow requires an active connection established by
vignette("dbi-advanced") for a walkthrough.
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
TRUEif no more rows are available for fetching.
Repeat the last four steps as necessary.
dbClearResult()to clean up the result set object. This step is mandatory even if no rows have been fetched or if an error has occurred during the processing. It is good practice to use
withr::defer()to ensure that this step is always executed.
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.