library(glue)
library(RPostgreSQL)
library(DBI)

drv <- dbDriver("PostgreSQL")
con <- dbConnect(drv,
                 host=Sys.getenv("JDBCURL"),
                 port = Sys.getenv("PORT"),
                 dbname = Sys.getenv("DBNAME"),
                 user = Sys.getenv("USER"),
                 password = Sys.getenv("PW"))

users_syntax <- "123, 1234, 12345"

query <- glue("
  INSERT INTO table_name (user_id)
  VALUES ({users})",
  users = users_syntax)
  %>% as.character

dbSendQuery(con, query)