danny0405 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_r309006316
##########
File path:
core/src/main/java/org/apache/calcite/rel/rel2sql/RelToSqlConverter.java
##########
@@ -195,15 +198,78 @@ public Result visit(Project e) {
final Builder builder =
x.builder(e, Clause.SELECT);
final List<SqlNode> selectList = new ArrayList<>();
+
+ final boolean checkNull = isCastNullNeeded(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();
}
+ /**
+ * Returns whether a NULL literal in the SELECT clause needs to be wrapped
in a CAST.
+ * @param stack stack of visit
+ * @return If null needs to be casted then return true, otherwise return
false.
+ * There are several cases to handle :
+ * 1. If a Project is under a Join or other operator which not instance of
SingleRel,
+ * and there may be some SingleRel which is not Project between the
project and none SingleRel,
+ * NULL needs to be wrapped in a CAST.
+ * Here is an example,
+ * "SELECT * FROM (SELECT CAST(NULL AS INT) AS c1, c2 FROM t1) AS t1
+ * JOIN (SELECT c3, c4 FROM t2) AS t2 ON c2 = c3"
+ *
+ * 2. If a Project is under another Project,
+ * and there may be some SingleRel which is not Project between these two
Project,
+ * NULL needs to be wrapped in a CAST.
+ * Here is an example,
+ * "SELECT * FROM (SELECT CAST(NULL AS INT) AS c1, c2 FROM t1) as t1
WHERE c2 = 10"
+ *
+ * 3. If a Project is under a TableModify,
+ * and there may be some SingleRel which is not Project between the
Project and TableModify,
+ * because that the type of NULL can be inferred by the target table of
TableModify,
+ * so NULL does not need to be wrapped in a CAST.
+ * Here is an example,
+ * "INSERT INTO t SELECT CAST(NULL AS INT) AS c1, c2 FROM t1"
Review comment:
What do you mean by "SingleRel", i didn't see any in your example.
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