Using Dates with RSQLite - r

Question

How do you write a SQL query with a date using RSQLite. Here is an example below. The dbGetQuery does not return any rows.
require(RSQLite)
require(ggplot2)
data(presidential)
m <- dbDriver("SQLite")
tmpfile <- tempfile('presidential', fileext='.db')
conn <- dbConnect(m, dbname=tmpfile)
dbWriteTable(conn, "presidential", presidential)
dbGetQuery(conn, "SELECT * FROM presidential WHERE Date(start) >= Date('1980-01-01')")

Answer 1

Just to illustrate, this works fine:
tmpfile <- tempfile('presidential', fileext='.db')
conn <- dbConnect(m, dbname=tmpfile)
p <- presidential
p$start <- as.character(p$start)
p$end <- as.character(p$end)
dbWriteTable(conn, "presidential", p)
dbGetQuery(conn, "SELECT * FROM presidential WHERE start >= '1980-01-01'")
You can read about the lack of native date types in SQLite in the docs here. I've been using strings as dates for so long in SQLite that I'd actually forgotten about the issue completely.
And yes, I've written a small R function that converts any Date column in a data frame to character. For simple comparisons, keeping them in YYYY-MM-DD is enough, and if I need to do arithmetic I convert them after the fact in R.

Answer 2

Following on from #joran's answer, here's a simple function to convert date columns to string for a data.frame.
mutate(df, across(where(is.Date), ~ format(.x, "%Y.%m.%d")))

Answer 3

I found working with RSQLite and dplyr to be the most convenient way to stay type-consistent using R and SQLite. In particular, extendend_types = TRUE ensures that columns of type DATE, DATETIME / TIMESTAMP, and TIME are mapped to the corresponding R-classes (at least after version 2.2.8 for RSQLite).
library(dplyr)
library(RSQLite)
library(ggplot2)
data(presidential)
mydb <- dbConnect(SQLite(), "presidential.sqlite", extended_types = TRUE)
dbWriteTable(mydb, "presidential", presidential)
tbl(mydb, "presidential") %>%
filter(start >= as.Date("1980-01-01")) %>%
collect()
You can also formulate the latter collection as a get query:
dbGetQuery(mydb, "SELECT * FROM presidential WHERE start >= CAST('1980-01-01' AS DATE)")

Answer 4

As #joran suggests keeping dates in text in SQLlite seems like the best way to go for the time being.
I used #Richard Knight's approach for conversion in, but with ISO format, to change the date to string before writing the dataframe:
local_df %>% mutate(across(where(lubridate::is.Date), ~ format(.x, "%Y-%m-%d")))
Manipulating the dates remotely can be done using sql translation, particularly:
remote_df %>% mutate(date_as_number = julianday(date_as_string))
remote_df %>% mutate(date_as_string = date(date_as_number))
N.b. that is date not as.Date in the second one. This is because as.Date will get translated to CAST(date_as_number AS DATE) whereas what we want is to use SQLLite's date() function with a floating point number as returned by julianday().
Mapping the remote datestrings back into dates can be done automatically, if you :
collect <- function(remote_df, ...) {
raw = remote_df %>% dplyr::collect(...)
isoDateString = function(x) return(is.character(x) & all(na.omit(stringr::str_detect(x,"[0-9]{4}-[0-9]{2}-[0-9]{2}"))) & !all(is.na(x)))
raw = raw %>% mutate(across(where(isoDateString), ~ as.Date(.x, "%Y-%m-%d")))
maybeJulian = function(x) {return(is.double(x) & all(na.omit(x>2440587.5)) & all(na.omit(x<2488069.5)) & !all(is.na(x)))}
raw = raw %>% mutate(across(matches(".*(D|d)ate.*") & where(maybeJulian), ~ as.Date(.x-2440587.5, "1970-01-01")))
return(raw)
}
The apparently random numbers in the maybeJulian function correspond to 1970-01-01 and 2100-01-01