Date Loop Query in R using DBI

Question

I have a query

library(DBI)
res = dbSendQuery(con,
       "select 
        X, Y, z from table where date between date'2018-07-01' - interval '31' day and date'2018-07-01 - interval '1' day")
res.df = dbFetch(res, -1)  

I want to run this on a date loop so that it populates the data for all dates between 2018-07-01 and 2018-07-30

Can someone please help me with the code for that

Answer 1

A loop isn't necessary to populate the data for all dates between 2018-07-01 and 2018-07-30.

You can just filter by dates:

res = dbSendQuery(con,
                  "select X, Y, z 
                  from table 
                  where date > '2018-06-31' 
                  and date < '2018-07-31'")
res.df = dbFetch(res, -1)  

Answer 2

If you really want a loop:

date_seq <- as.character(seq(as.Date("2017-07-01"), 
                             as.Date("2017-07-30"), by = "day"))

for (i in 1:length(date_seq)) {
  string <- "select X, Y, z from table where date between date'REPLACEME' - interval '31' day and date'REPLACEME' - interval '1' day"
  string <- gsub("REPLACEME", date_seq[i], string)
  print(string) # replace this with the dbSendQuery
}

[1] "select X, Y, z from table where date between date'2017-07-01' - interval '31' day and date'2017-07-01' - interval '1' day"
[1] "select X, Y, z from table where date between date'2017-07-02' - interval '31' day and date'2017-07-02' - interval '1' day"
...
[1] "select X, Y, z from table where date between date'2017-07-30' - interval '31' day and date'2017-07-30' - interval '1' day"