uros-b commented on code in PR #57476:
URL: https://github.com/apache/spark/pull/57476#discussion_r3700460927
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sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/mathExpressions.scala:
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@@ -1971,6 +1971,47 @@ case class BRound(
newLeft: Expression, newRight: Expression): BRound = copy(child = newLeft,
scale = newRight)
}
+/**
+ * Truncate an expression toward zero to `scale` decimal places.
+ * A negative `scale` truncates digits to the left of the decimal point.
+ * truncate(1234.5678, 2) = 1234.56, truncate(-1234.5678, 2) = -1234.56.
+ */
+// scalastyle:off line.size.limit
+@ExpressionDescription(
+ usage = "_FUNC_(expr[, scale]) - Returns `expr` truncated toward zero to
`scale` decimal places. `scale` defaults to 0. A negative `scale` truncates
digits to the left of the decimal point.",
+ arguments = """
+ Arguments:
+ * expr - The expression to truncate. An expression that evaluates to a
numeric.
+ * scale - The number of decimal places to keep. An expression that
evaluates to an integer, must be a constant, and defaults to 0. A negative
value truncates digits to the left of the decimal point.
+ """,
+ examples = """
+ Examples:
+ > SELECT _FUNC_(1234.5678, 2);
+ 1234.56
+ > SELECT _FUNC_(1234.5678, -2);
+ 1200
+ > SELECT _FUNC_(-1234.5678, 2);
+ -1234.56
+ """,
+ since = "4.3.0",
+ group = "math_funcs")
+// scalastyle:on line.size.limit
+case class Truncate(
+ child: Expression,
+ scale: Expression,
+ override val ansiEnabled: Boolean = SQLConf.get.ansiEnabled)
+ extends RoundBase(child, scale, BigDecimal.RoundingMode.DOWN, "ROUND_DOWN") {
Review Comment:
RoundBase.dataType widens decimals by one integral digit because rounding
can carry (ceil(9.9, 0) = 10). Truncation never can, so truncate(1234.5678, 2)
returns decimal(7,2) where decimal(6,2) would do. Inheriting this is the safe
choice, but a comment noting it's deliberate would help the next reader, since
it can matter at MAX_PRECISION.
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