La query MySQL funziona bene su workbench ma impiega troppo tempo in r

La soluzione potrebbe essere sostituire dbGetQuery con dbSendQuery e dbFetch chiamata.

I semplici passaggi potrebbero essere:

library(RMySQL)

# From OP
con <- dbConnect(RMySQL::MySQL(),
               dbname ="mydb",
               host      = "localhost",
               port  = 3306,
               user  = "root",
               password = "")

# iterationresults is a table in your database. One can replace query with his own
rs = dbSendQuery(con, "select * from iterationresults")

# Fetch first 20 rows and repeat it for all rows  
df = dbFetch(rs, n=20)

# For repeated call
while (!dbHasCompleted(rs)){
 df<- dbFetch(rs, n=20)
}
# OR Fetch all rows in one go
df = dbFetch(rs, n=-1)

# Free all resources
dbClearResult(rs) 
# Close connection
dbDisconnect(con)
# df will contain results i.e.
df
#   ID Truck_ID Speed trip_id
#1  11  TTI 039     6     217
#2  12  TTI 039     6     217
# ........