[FLINK-34656] Generated code for `ITEM` operator should return null when getting element of a null map/array/row

• Type: Bug
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 1.20.0
• Component/s: Table SQL / Planner
• Assignee: Unassigned
• Reporter: yisha zhou
• Created: 12/Mar/24 13:58
• Updated: 28/Mar/24 05:08

Description

In FieldAccessFromTableITCase we can find that the expected result of f0[1] is null when f0 is a null array. 

However, behavior in generated code for ITEM is not consistent with case above. The main code is:

 

val arrayAccessCode =
  s"""
     |${array.code}
     |${index.code}
     |boolean $nullTerm = ${array.nullTerm} || ${index.nullTerm} ||
     |   $idxStr < 0 || $idxStr >= ${array.resultTerm}.size() || $arrayIsNull;
     |$resultTypeTerm $resultTerm = $nullTerm ? $defaultTerm : $arrayGet;
     |""".stripMargin 

If `array.nullTerm` is true, a default value of element type will be returned, for example -1 for null bigint array.

The reason why FieldAccessFromTableITCase can get expected result is that the 
ReduceExpressionsRule generated an expression code for that case like:

boolean isNull$0 = true || false ||
   ((int) 1) - 1 < 0 || ((int) 1) - 1 >= ((org.apache.flink.table.data.ArrayData) null).size() || ((org.apache.flink.table.data.ArrayData) null).isNullAt(((int) 1) - 1);
long result$0 = isNull$0 ? -1L : ((org.apache.flink.table.data.ArrayData) null).getLong(((int) 1) - 1);
if (isNull$0) {
  out.setField(0, null);
} else {
  out.setField(0, result$0);
} 

The reduced expr will be a null literal.
 

I think the behaviors for getting element of a null value should be unified.