# Generate SQL expression for window function
# over("avg(x)", frame = c(-Inf, 0))
# over("avg(x)", order = "y")
# over("avg(x)", order = c("x", "y"))
# over("avg(x)")
over <- function(expr, partition = NULL, order = NULL, frame = NULL) {
if (length(partition) == 0) {
partition <- NULL
}
if (!is.null(partition)) {
if (!is.sql(partition)) {
partition <- ident(partition)
}
partition <- build_sql("PARTITION BY ",
sql_vector(escape(partition, con = partition_con()), collapse = ", ", parens = FALSE))
}
if (!is.null(order)) {
if (!is.sql(order)) {
order <- ident(order)
}
order <- build_sql("ORDER BY ", sql_vector(escape(order), collapse = ", ", parens = FALSE))
}
if (!is.null(frame)) {
if (is.null(order)) {
warning(
"Windowed expression '", expr, "' does not have explicit order.\n",
"Please use arrange() to make determinstic.",
call. = FALSE
)
}
if (is.numeric(frame)) frame <- rows(frame[1], frame[2])
frame <- build_sql("ROWS ", frame)
}
over <- sql_vector(compact(list(partition, order, frame)), parens = TRUE)
sql <- build_sql(expr, " OVER ", over)
sql
}
rows <- function(from = -Inf, to = 0) {
if (from >= to) stop("from must be less than to", call. = FALSE)
dir <- function(x) if (x < 0) "PRECEDING" else "FOLLOWING"
val <- function(x) if (is.finite(x)) as.integer(abs(x)) else "UNBOUNDED"
bound <- function(x) {
if (x == 0) return("CURRENT ROW")
paste(val(x), dir(x))
}
if (to == 0) {
sql(bound(from))
} else {
sql(paste0("BETWEEN ", bound(from), " AND ", bound(to)))
}
}
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