From 8b6ba5a2e0e8067008cb75a631c94af67624e4e5 Mon Sep 17 00:00:00 2001
From: JiaKe <ke.a.jia@intel.com>
Date: Wed, 4 Jan 2023 08:56:29 +0000
Subject: [PATCH] Fix the result mismatch for right expression (#107)

---
 velox/functions/prestosql/StringFunctions.h | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/velox/functions/prestosql/StringFunctions.h b/velox/functions/prestosql/StringFunctions.h
index 00c71690be08a..7c47fda704e99 100644
--- a/velox/functions/prestosql/StringFunctions.h
+++ b/velox/functions/prestosql/StringFunctions.h
@@ -349,6 +349,13 @@ struct SubstrFunction {
     if (start < 0) {
       start = numCharacters + start + 1;
     }
+    
+    // Following vanilla spark semantics. When the start is 0 after adjusing start,
+    // Keep the origin input. 
+    if (start <= 0) {
+      start = 1;
+      length = numCharacters;
+    }
 
     // Following Presto semantics
     if (start <= 0 || start > numCharacters || length <= 0) {