dbplyr mutate character to date format in temp table

Question

I have extracted data to a temporary table in SQL Server using DBI::dbGetQuery.

Even though, in the real query (not the play query below), I select convert(date, date_value) as date_value, the dates are still stored as character.

I then try to mutate the character representing the date using lubridate::ymd, however I obtain a message saying

date_value not found

I have also tried, convert(date, date_value) and as.Date to no avail.

require(dplyr)
if (dbExistsTable(con, "##temp", catalog_name = "tempdb")){
  dbRemoveTable(con, "##temp")
}
DBI::dbGetQuery(con, paste(              
"select 
    convert(date, '2013-05-25') as date_value
into ##temp
"))

tbl(con, "##temp")

# Error - date_value not found
tbl(con, "##temp") %>%   mutate(date_value= lubridate::ymd(date_value))

# this works
tbl(con, "##temp") %>%   mutate(temp= date_value) 

# this doesn't work - date value not found
tbl(con, "##temp") %>%   mutate(temp= lubridate::ymd(date_value))

How can I work this field as a date?

Note: When I write the following in SQL Server, date_value shows as a date Type

select 
convert(date, '2013-05-25') as date_value
into #hello

select *
from #hello

exec tempdb..sp_help #hello

in response to the comment from @Kevin Arseneau, the following image shows the results from executing a show_query()

Answer 1

Some months ago I was looking a solution for use lubridate functions + dplyr on PostgreSQL unsuccessfully. Accidentally I found the easy solution using DBMS functions directly on dbplyr coding.

Sorry, I will use PostgreSQL example because I don't know about SQL server functions. In this example I will create a temporal table in a PostgreSQL DBMS, then I will compute a new column with the function to_date() provided by PostgreSQL. The result is the date that was looking for:

# Easy example on postgreSQL
library(tidyverse)
library(dbplyr)
library(RPostgreSQL)

con <- dbConnect(PostgreSQL(), 
                 dbname="postgre",
                 host="localhost",
                 port=5432,
                 user="user",
                 password="pass")

date <- data_frame(date_str = c("20180212", "20180213"))

dbWriteTable(con, "tmp", date, temporary = TRUE)

tbl(con, "tmp") %>% 
# The DBMS function is used here
  mutate(date = to_date(date_str, "YYYYMMDD")) %>% 
# Finally, I collect the data from database to R session
  collect()

#># A tibble: 2 x 3
#>  row.names date_str date      
#>* <chr>     <chr>    <date>    
#>1 1         20180212 2018-02-12
#>2 2         20180213 2018-02-13

You can try with settings for SQL Server, and the CAST() function could convert your strings to date, as is explained in this answer. I hope this help you.

I hope someday dplyr/dbplyr can translate the lubridate functions into SQL queries.