Nothing
#' Backend: Teradata
#'
#' @description
#' See `vignette("translation-function")` and `vignette("translation-verb")` for
#' details of overall translation technology. Key differences for this backend
#' are:
#'
#' * Uses `TOP` instead of `LIMIT`
#' * Selection of user supplied translations
#'
#' Use `simulate_teradata()` with `lazy_frame()` to see simulated SQL without
#' converting to live access database.
#'
#' @name backend-teradata
#' @aliases NULL
#' @examples
#' library(dplyr, warn.conflicts = FALSE)
#'
#' lf <- lazy_frame(a = TRUE, b = 1, c = 2, d = "z", con = simulate_teradata())
#' lf %>% head()
NULL
#' @export
#' @rdname backend-teradata
simulate_teradata <- function() simulate_dbi("Teradata")
#' @export
dbplyr_edition.Teradata <- function(con) {
2L
}
#' @export
sql_query_select.Teradata <- function(con,
select,
from,
where = NULL,
group_by = NULL,
having = NULL,
window = NULL,
order_by = NULL,
limit = NULL,
distinct = FALSE,
...,
subquery = FALSE,
lvl = 0) {
# #685
# https://docs.teradata.com/r/2_MC9vCtAJRlKle2Rpb0mA/frQm7Rn09FJZZLQAuaUvJA
# You cannot specify these options in a SELECT statement that specifies the TOP n operator:
# * DISTINCT option
# * QUALIFY clause
# * SAMPLE clause
# * WITH clause
limit_needs_subquery <- is_true(distinct)
if (!is_null(limit) && limit_needs_subquery) {
unlimited_query <- sql_select_clauses(con,
select = sql_clause_select(con, select, distinct, top = NULL),
from = sql_clause_from(from),
where = sql_clause_where(where),
group_by = sql_clause_group_by(group_by),
having = sql_clause_having(having),
window = sql_clause_window(window),
order_by = sql_clause_order_by(order_by, subquery, limit = NULL),
lvl = lvl + 1
)
alias <- unique_subquery_name()
from <- sql_query_wrap(con, unlimited_query, name = alias)
select_outer <- sql_star(con, alias)
out <- sql_select_clauses(con,
select = sql_clause_select(con, select_outer, distinct = FALSE, top = limit),
from = sql_clause_from(from),
where = NULL,
group_by = NULL,
having = NULL,
window = NULL,
order_by = NULL,
lvl = lvl
)
return(out)
}
sql_select_clauses(con,
select = sql_clause_select(con, select, distinct, top = limit),
from = sql_clause_from(from),
where = sql_clause_where(where),
group_by = sql_clause_group_by(group_by),
having = sql_clause_having(having),
window = sql_clause_window(window),
order_by = sql_clause_order_by(order_by, subquery, limit),
lvl = lvl
)
}
#' @export
sql_translation.Teradata <- function(con) {
sql_variant(
sql_translator(.parent = base_odbc_scalar,
`!=` = sql_infix("<>"),
bitwNot = sql_prefix("BITNOT", 1),
bitwAnd = sql_prefix("BITAND", 2),
bitwOr = sql_prefix("BITOR", 2),
bitwXor = sql_prefix("BITXOR", 2),
bitwShiftL = sql_prefix("SHIFTLEFT", 2),
bitwShiftR = sql_prefix("SHIFTRIGHT", 2),
as.numeric = function(x, digits = 9L) {
digits <- vctrs::vec_cast(digits, integer())
sql_expr(CAST(!!x %as% DECIMAL(12L, !!digits)))
},
as.double = sql_cast("NUMERIC"),
as.character = sql_cast("VARCHAR(MAX)"),
as.Date = teradata_as_date,
log10 = sql_prefix("LOG"),
log = sql_log(),
cot = sql_cot(),
quantile = sql_quantile("APPROX_PERCENTILE"),
median = sql_median("APPROX_PERCENTILE"),
nchar = sql_prefix("CHARACTER_LENGTH"),
ceil = sql_prefix("CEILING"),
ceiling = sql_prefix("CEILING"),
atan2 = function(x, y) {
sql_expr(ATAN2(!!y, !!x))
},
substr = function(x, start, stop) {
len <- stop - start + 1
sql_expr(SUBSTR(!!x, !!start, !!len))
},
startsWith = function(string, pattern) {
glue_sql2(sql_current_con(), "CAST(CASE WHEN INSTR({.val string}, {.val pattern}) = 1 THEN 1 ELSE 0 END AS INTEGER)")
},
paste = sql_paste_infix(" ", "||", function(x) sql_expr(!!x)),
paste0 = sql_paste_infix("", "||", function(x) sql_expr(!!x)),
row_number = win_rank("ROW_NUMBER", empty_order = TRUE),
# lubridate ---------------------------------------------------------------
# https://en.wikibooks.org/wiki/SQL_Dialects_Reference/Functions_and_expressions/Date_and_time_functions
as_date = teradata_as_date,
week = function(x){
sql_expr(WEEKNUMBER_OF_YEAR(!!x, 'iso'))
},
quarter = function(x) {
glue_sql2(sql_current_con(), "to_char({.val x}, 'q')")
}
),
sql_translator(.parent = base_odbc_agg,
var = sql_aggregate("VAR_SAMP", "var"),
row_number = win_rank("ROW_NUMBER", empty_order = TRUE),
weighted.mean = function(x, w, na.rm = T) {
# nocov start
win_over(
sql_expr(SUM((!!x * !!w))/SUM(!!w)),
win_current_group(),
win_current_group(),
win_current_frame()
)
# nocov end
}
),
sql_translator(.parent = base_odbc_win,
var = win_recycled("VAR_SAMP"),
row_number = win_rank("ROW_NUMBER", empty_order = TRUE),
lead = function(x, n = 1L, default = NA, order_by = NULL) {
win_over(
sql_expr(LEAD(!!x, !!n, !!default)),
win_current_group(),
order_by %||% win_current_group(),
win_current_frame()
)
},
lag = function(x, n = 1L, default = NA, order_by = NULL) {
win_over(
sql_expr(LAG(!!x, !!as.integer(n), !!default)),
win_current_group(),
order_by %||% win_current_group(),
win_current_frame()
)
},
cumsum = function(x, order_by = NULL, frame = c(-Inf, 0)) {
win_over(
sql_expr(SUM(!!x)),
win_current_group(),
order_by %||% win_current_group(),
frame %||% win_current_frame()
)
},
weighted.mean = function(x, w, na.rm = T) {
# nocov start
win_over(
sql_expr(SUM((!!x * !!w))/SUM(!!w)),
win_current_group(),
win_current_group(),
win_current_frame()
)
# nocov end
}
)
)
}
teradata_as_date <- function(x) {
xq <- enquo(x)
x_expr <- quo_get_expr(xq)
if (is.character(x_expr) && !is.sql(x_expr)) {
glue_sql2(sql_current_con(), "DATE {.val x}")
} else {
sql_cast("DATE")(x)
}
}
#' @export
sql_table_analyze.Teradata <- function(con, table, ...) {
# https://www.tutorialspoint.com/teradata/teradata_statistics.htm
glue_sql2(con, "COLLECT STATISTICS {.tbl table}")
}
utils::globalVariables(c("ATAN2", "SUBSTR", "DECIMAL", "WEEKNUMBER_OF_YEAR", "SUM"))
#' @export
#' @rdname win_over
win_rank_tdata <- function(f) {
lifecycle::deprecate_warn(
"2.4.0",
what = "win_rank_tdata()",
with = "win_rank()"
)
force(f)
function(order_by = NULL) {
order_by <- order_by %||% win_current_group()
if (is_empty(order_by)) order_by <- sql("(SELECT NULL)")
win_over(
sql(glue("{f}()")),
partition = win_current_group(),
order = order_by,
frame = win_current_frame()
)
}
}
Any scripts or data that you put into this service are public.
Add the following code to your website.
For more information on customizing the embed code, read Embedding Snippets.