From 9b6b51254098e3ae72dea161edee547a10d87d44 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 5aa7a10bec472..57781f31318fe 100644
--- a/velox/functions/prestosql/StringFunctions.h
+++ b/velox/functions/prestosql/StringFunctions.h
@@ -104,6 +104,13 @@ 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) {