After Connecting, you can execute a SQL statement and retrieve the results.

SELECT Procedure

You can use the sqlQuery function to execute queries. By default, it will return all the results as a single data frame. This works well for smaller result sets.

results <- sqlQuery(cnx, "SELECT ShipName, ShipCity FROM \"postgres\".\"public\".Orders WHERE ShipCountry = 'USA'")
for (row in 1:nrow(results)) {
    cat(paste("ShipName = ", results[row,]$ShipName, "\n"))
    cat(paste("ShipCity = ", results[row,]$ShipCity, "\n"))
}

Iterating over the Results

For larger result sets, sqlQuery can return results in batches instead of storing the entire result set in memory. When there are no results left, or an error occurs, sqlQuery and sqlGetResults will return an integer error code instead of a data frame.

results <- sqlQuery(cnx, "SELECT ShipName, ShipCity FROM \"postgres\".\"public\".Orders WHERE ShipCountry = 'USA'", max = 1000)
while (is.data.frame(results)) {
    for (row in 1:nrow(results)) {
        cat(paste("ShipName = ", results[row,]$ShipName))
        cat(paste("ShipCity = ", results[row,]$ShipCity))
    }
    rows <- sqlGetResults(cnx, max = 1000)
}