[GitHub] [flink] twalthr commented on a change in pull request #12857: [FLINK-18520][table] Fix unresolvable catalog table functions

[GitBox <gi...@apache.org>]

twalthr commented on a change in pull request #12857:
URL: https://github.com/apache/flink/pull/12857#discussion_r452026790



##########
File path: flink-table/flink-table-planner-blink/src/main/java/org/apache/flink/table/planner/catalog/FunctionCatalogOperatorTable.java
##########
@@ -208,11 +209,17 @@ private boolean verifyFunctionKind(
 		// it would be nice to give a more meaningful exception when a scalar function is used instead
 		// of a table function and vice versa, but we can do that only once FLIP-51 is implemented
 
-		if (definition.getKind() == FunctionKind.SCALAR &&
-				(category == SqlFunctionCategory.USER_DEFINED_FUNCTION || category == SqlFunctionCategory.SYSTEM)) {
+		if (definition.getKind() == FunctionKind.SCALAR) {
+			if (category != null && category.isTableFunction()) {
+				throw new ValidationException(
+					String.format(
+						"Function '%s' cannot be used as a table function.",
+						identifier.asSummaryString()
+					)
+				);
+			}
 			return true;
-		} else if (definition.getKind() == FunctionKind.TABLE &&
-				(category == SqlFunctionCategory.USER_DEFINED_TABLE_FUNCTION || category == SqlFunctionCategory.SYSTEM)) {
+		} else if (definition.getKind() == FunctionKind.TABLE) {

Review comment:
       Unfortunately, the category field is not very useful. That was also the cause for this bug. It seems that when you use a catalog function, this becomes just `USER_DEFINED_FUNCTION`. So we can't have a better exception right now.




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