From b85cb0071bab7e37cc55f1629d3e2bc3ad0b9dcb Mon Sep 17 00:00:00 2001
From: EmmyMiao87 <522274284@qq.com>
Date: Sun, 8 Sep 2019 21:26:31 +0800
Subject: [PATCH] Bug-fix: error result of union stmt (#1758)

ISSUES-1725: The result of union stmt whose child is outer join stmt is incorrect.

Example:
sql: (select k1 from empty) union all (select b.k1 k1 from left_table a left join empty  b on a.k2 = b.k2);
context: the empty table has no data.
error result: 0
expect result: null

Reason:
The judgment (columns k1 who belongs to union tuple is nullable ) is incorrect.
It could not be determined by slot attribute of children when the slot is produced by the outer join.
The slot A is not nullable while the result of outer join is nullable which is same as slot A.
So, the judgment needs to consider if the slot is come from the outer join.
---
 fe/src/main/java/org/apache/doris/analysis/UnionStmt.java | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fe/src/main/java/org/apache/doris/analysis/UnionStmt.java b/fe/src/main/java/org/apache/doris/analysis/UnionStmt.java
index ca14097157..f123db3f0b 100644
--- a/fe/src/main/java/org/apache/doris/analysis/UnionStmt.java
+++ b/fe/src/main/java/org/apache/doris/analysis/UnionStmt.java
@@ -451,7 +451,8 @@ public class UnionStmt extends QueryStmt {
                 Expr resultExpr = op.getQueryStmt().getResultExprs().get(i);
                 slotDesc.addSourceExpr(resultExpr);
                 SlotRef slotRef = resultExpr.unwrapSlotRef(false);
-                if (slotRef == null || slotRef.getDesc().getIsNullable()) isNullable = true;
+                if (slotRef == null || slotRef.getDesc().getIsNullable()
+                        || analyzer.isOuterJoined(slotRef.getDesc().getParent().getId())) isNullable = true;
                 if (op.hasAnalyticExprs()) continue;
                 slotRef = resultExpr.unwrapSlotRef(true);
                 if (slotRef == null) continue;