RODBC loses time values of datetime when result set is large

Question

So this is VERY strange. RODBC seems to drop the time portion of DateTime SQL columns if the result set is large enough. (The queries are running against an SQL S

Answer 1

I think this is a case of times being stripped from the dates where the date range includes shifts to/from daylight savings time. If you are selecting periods that don't include daylight savings shifts, the times will be retained (e.g., from 1/1/2007 to 3/1/2007. This could possibly be avoided by changing the system time on your computer to follow a time zone (e.g., Arizona) where there are no daylight savings shifts (sounds bizarre, but it has worked for me).

To overcome this issue, import the DateTimes as characters (using "as.is") and then convert them to POSIXct. You could alternatively use "strptime" which converts to POSIXlt and allows you to specify the format. Here's an example of a SQL query where DateTimes are imported as.is (TRUE), but asociated DataValues are not (FALSE) and then the DateTime is converted to an R date format:

data <- sqlQuery(channel, paste("SELECT LocalDateTime, DataValue FROM DataValues WHERE  LocalDateTime >= '1/1/2007 0:00' AND LocalDateTime < '1/1/2008 0:00' ORDER BY LocalDateTime ASC"),as.is=c(TRUE,FALSE))

data$LocalDateTime <- as.POSIXct(totalP$LocalDateTime,tz="MST")