Trying to understand how to use query parameters in Shiny

test.R

library(shiny)
library(RMySQL)

source("keys.R")

con <- dbConnect( MySQL(), user=login, password=pass, db=database, host=host)
print(paste("Default:", groupId))
res <- dbSendQuery(con, paste('SELECT user_id, user_name
                   FROM info i , enrolment e 
                   where i.user_id = e.fk_user_id and e.fk_group_id = ', groupId))
dataf <- dbFetch(res)
lista <- as.list(setNames(dataf$user_id, dataf$user_name))
dbClearResult(res)
dbDisconnect(con)

ui <- fluidPage( column(3, checkboxGroupInput("users", 
                                label = h3("User IDs"), 
                                choices = lista, 
                                selected = dataf$user_id),
             verbatimTextOutput("value")
      ))

server <- function(input, output, session) {
  observe({
  groupId <- parseQueryString(session$clientData$url_search)
  if ( length(groupId) > 0) {
    print(paste("groupId:",groupId))
  }})
}

shinyApp(ui = ui, server = server)