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_r309006898
##########
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"
+ *
+ * Please note that in the example mentioned above,
+ * the Project converted by the select statement with "CAST(NULL AS INT)"
+ * is with no CAST call but a NULL expression and a data type described in
RowType.
+ */
+ private static boolean isCastNullNeeded(Deque<Frame> stack) {
+ final int stackSize = stack.size();
+ for (int i = 1; i < stackSize; i++) {
+ RelNode currentNode = Iterables.get(stack, i).r;
+ if (!(currentNode instanceof SingleRel)) {
+ break;
+ } else if (currentNode instanceof Project) {
+ // direct or indirect input of Project need to cast null type
+ break;
+ } else if (currentNode instanceof TableModify) {
+ // direct or indirect input of TableModify do not need to cast null
type
+ return false;
+ }
+ }
+
+ return true;
+ }
+
+ /**
+ * cast null with type
+ * @param sqlNodeNull null SqlNode
+ * @param field field description of sqlNodeNull
+ * @return SqlNode with cast to type.
+ */
+ private SqlNode castNullType(SqlNode sqlNodeNull, RelDataTypeField field) {
Review comment:
/**
* Wrap the {code sqlNodeNull} in a CAST operator with target type as
{code field}.
* @param sqlNodeNull null literal
* @param field field description of sqlNodeNull
* @return null literal wrapped in CAST call.
*/
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