urosstan-db commented on code in PR #57564:
URL: https://github.com/apache/spark/pull/57564#discussion_r3657507698
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sql/core/src/main/scala/org/apache/spark/sql/jdbc/JdbcDialects.scala:
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@@ -442,7 +442,17 @@ abstract class JdbcDialect extends Serializable with
Logging {
override def visitCast(expr: String, exprDataType: DataType, dataType:
DataType): String = {
val databaseTypeDefinition =
getJDBCType(dataType).map(_.databaseTypeDefinition).getOrElse(dataType.typeName)
- s"CAST($expr AS $databaseTypeDefinition)"
+ // Spark truncates toward zero when casting a fractional value to an
integral type, but many
+ // databases round instead, so a pushed down cast can return a different
result than Spark.
+ // Dialects for such databases override `truncateFractionalValue` to
truncate the value first.
+ val castedExpr = if (exprDataType.isInstanceOf[FractionalType] &&
+ dataType.isInstanceOf[IntegralType] &&
+
!SQLConf.get.getConf(SQLConf.LEGACY_JDBC_ROUND_INTEGRAL_CAST_PUSHDOWN)) {
+ truncateFractionalValue(expr)
Review Comment:
nit: Do we need to fix this on v2 expression builder level? Other data
sources may benefit of stricter API for this truncation fix.
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