Github user jinfengni commented on a diff in the pull request:
https://github.com/apache/drill/pull/452#discussion_r57998932
--- Diff:
exec/java-exec/src/main/java/org/apache/drill/exec/expr/fn/impl/DateTypeFunctions.java
---
@@ -40,6 +42,41 @@
public class DateTypeFunctions {
+ /**
+ * Function to check if a varchar value can be cast to a date.
+ *
+ * At the time of writing this function, several other databases were
checked
+ * for behavior compatibility. There was not a consensus between
oracle and
+ * Sql server about the expected behavior of this function, and
Postgres
+ * lacks it completely.
+ *
+ * Sql Server appears to have both a DATEFORMAT and language locale
setting
+ * that can change the values accepted by this function. Oracle
appears to
+ * support several formats, some of which are not mentioned in the Sql
+ * Server docs. With the lack of standardization, we decided to
implement
+ * this function so that it would only consider date strings that
would be
+ * accepted by the cast function as valid.
+ */
+ @SuppressWarnings("unused")
+ @FunctionTemplate(name = "isdate", scope =
FunctionTemplate.FunctionScope.SIMPLE, nulls=NullHandling.INTERNAL,
+ costCategory = FunctionTemplate.FunctionCostCategory.COMPLEX)
+ public static class CastVarCharToDate implements DrillSimpleFunc {
+
+ @Param NullableVarCharHolder in;
--- End diff --
Do we need an implementation for non-nullable input, since it's using
NullHandling.INTERNAL?
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