[GitHub] [calcite] weidong3630 commented on a change in pull request #1338: [CALCITE-3210] Fix the bug that RelToSqlConverter converts "cast(null as $type)" just as null

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weidong3630 commented on a change in pull request #1338: [CALCITE-3210] Fix the bug that RelToSqlConverter converts "cast(null as $type)" just as null
URL: https://github.com/apache/calcite/pull/1338#discussion_r308111011
 
 

 ##########
 File path: core/src/main/java/org/apache/calcite/rel/rel2sql/RelToSqlConverter.java
 ##########
 @@ -195,15 +198,57 @@ public Result visit(Project e) {
     final Builder builder =
         x.builder(e, Clause.SELECT);
     final List<SqlNode> selectList = new ArrayList<>();
+
+    boolean checkNull = isNeedCastNull(stack);
     for (RexNode ref : e.getChildExps()) {
       SqlNode sqlExpr = builder.context.toSql(null, ref);
+      if (checkNull && SqlUtil.isNullLiteral(sqlExpr, false)) {
+        sqlExpr = castNullType(sqlExpr, e.getRowType().getFieldList().get(selectList.size()));
+      }
       addSelect(selectList, sqlExpr, e.getRowType());
     }
 
     builder.setSelect(new SqlNodeList(selectList, POS));
     return builder.result();
   }
 
+  /**
+   * Check whether null item in select need to be casted
+   * @param stack stack of visit
+   * @return If null need to be casted then return true, otherwise return false.
+   */
+  private static boolean isNeedCastNull(Deque<Frame> stack) {
+    final int stackSize = stack.size();
+    if (stackSize > 1) {
 
 Review comment:
   1. Yes, "if" indeed need to be removed.
   2. I think stackSize is needed because that there is extra computation in  java.util.ArrayDeque#size

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