Make a select columns node (not a relational operation).

Source: R/select_columns.R

Make a select columns node (not a relational operation).

select_columns(source, columns, env = parent.frame())

Arguments

source

source to select from.
columns

list of distinct column names.
env

environment to look to.

Value

select columns node.

Examples


if (requireNamespace("DBI", quietly = TRUE) && requireNamespace("RSQLite", quietly = TRUE)) {
  my_db <- DBI::dbConnect(RSQLite::SQLite(), ":memory:")
  d <- rq_copy_to(my_db, 'd',
                   data.frame(AUC = 0.6, R2 = 0.2))
  optree <- select_columns(d, 'AUC')
  cat(format(optree))
  sql <- to_sql(optree, my_db)
  cat(sql)
  print(DBI::dbGetQuery(my_db, sql))
  DBI::dbDisconnect(my_db)
}

#> mk_td("d", c(
#>   "AUC",
#>   "R2")) %.>%
#>  select_columns(., 
#>     c('AUC'))
#> SELECT
#>  `AUC`
#> FROM (
#>  SELECT
#>   `AUC`
#>  FROM
#>   `d`
#> ) tsql_75049543662614518432_0000000000
#>   AUC
#> 1 0.6