[GitHub] [spark] AngersZhuuuu commented on a change in pull request #26053: [SPARK-29379][SQL]SHOW FUNCTIONS show '!=', '<>' , 'between', 'case'

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AngersZhuuuu commented on a change in pull request #26053: [SPARK-29379][SQL]SHOW FUNCTIONS  show '!=', '<>' , 'between', 'case'
URL: https://github.com/apache/spark/pull/26053#discussion_r335314222
 
 

 ##########
 File path: sql/core/src/main/scala/org/apache/spark/sql/execution/command/functions.scala
 ##########
 @@ -73,6 +73,11 @@ case class CreateFunctionCommand(
       s"is not allowed: '${databaseName.get}'")
   }
 
+  // Redefine a virtual function is not allowed
+  if (FunctionsCommand.virtualOperators.contains(functionName.toLowerCase(Locale.ROOT))) {
+    throw new AnalysisException(s"It's not allowed to redefine virtual function '$functionName'")
 
 Review comment:
   > what's the error message if users try to redefine `=`?
   
   can't use `create function = ....`, since `=` is a reserved key, we should use 
   ```
   create function `=` ....
   ```
   
   Error message:
   ```
   org.apache.hadoop.hive.ql.metadata.HiveException: InvalidObjectException(message:= is not a valid object name);
   org.apache.hadoop.hive.ql.metadata.HiveException: InvalidObjectException(message:> is not a valid object name);
   org.apache.hadoop.hive.ql.metadata.HiveException: InvalidObjectException(message:!= is not a valid object name);
   
   but `case` `between` can be registered.
   ```
   
   as @HyukjinKwon  methoned, we should fix this ambiguity between functions and operators at the end.

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