maropu commented on a change in pull request #30260:
URL: https://github.com/apache/spark/pull/30260#discussion_r522043708
##########
File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Cast.scala
##########
@@ -1770,6 +1782,110 @@ case class AnsiCast(child: Expression, dataType:
DataType, timeZoneId: Option[St
copy(timeZoneId = Option(timeZoneId))
override protected val ansiEnabled: Boolean = true
+
+ override def canCast(from: DataType, to: DataType): Boolean =
AnsiCast.canCast(from, to)
+}
+
+object AnsiCast {
+ /**
+ * As per section 6.13 "cast specification" in "Information technology —
Database languages " +
+ * "- SQL — Part 2: Foundation (SQL/Foundation)":
+ * If the <cast operand> is a <value expression>, then the valid
combinations of TD and SD
+ * in a <cast specification> are given by the following table. “Y” indicates
that the
+ * combination is syntactically valid without restriction; “M” indicates
that the combination
+ * is valid subject to other Syntax Rules in this Sub- clause being
satisfied; and “N” indicates
+ * that the combination is not valid:
+ * SD TD
+ * EN AN C D T TS YM DT BO UDT B RT CT RW
+ * EN Y Y Y N N N M M N M N M N N
+ * AN Y Y Y N N N N N N M N M N N
+ * C Y Y Y Y Y Y Y Y Y M N M N N
+ * D N N Y Y N Y N N N M N M N N
+ * T N N Y N Y Y N N N M N M N N
+ * TS N N Y Y Y Y N N N M N M N N
+ * YM M N Y N N N Y N N M N M N N
+ * DT M N Y N N N N Y N M N M N N
+ * BO N N Y N N N N N Y M N M N N
+ * UDT M M M M M M M M M M M M M N
+ * B N N N N N N N N N M Y M N N
+ * RT M M M M M M M M M M M M N N
+ * CT N N N N N N N N N M N N M N
+ * RW N N N N N N N N N N N N N M
+ *
+ * Where:
+ * EN = Exact Numeric
+ * AN = Approximate Numeric
+ * C = Character (Fixed- or Variable-Length, or Character Large Object)
+ * D = Date
+ * T = Time
+ * TS = Timestamp
+ * YM = Year-Month Interval
+ * DT = Day-Time Interval
+ * BO = Boolean
+ * UDT = User-Defined Type
+ * B = Binary (Fixed- or Variable-Length or Binary Large Object)
+ * RT = Reference type
+ * CT = Collection type
+ * RW = Row type
+ *
+ * Spark's ANSI mode follows the syntax rules, except it specially allow the
following
+ * straightforward type conversions which are disallowed as per the SQL
standard:
+ * - Numeric <=> Boolean
+ * - String <=> Binary
Review comment:
How about describing the special case above in
`sql-ref-ansi-compliance.md`, too?
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