From e7b43b8299337c02229885c8e757f8e9228c879c Mon Sep 17 00:00:00 2001
From: Alexey Antipovsky <alexey.vladimirovich@mariadb.com>
Date: Wed, 16 Dec 2020 22:39:46 +0300
Subject: [PATCH] MCOL-4455 Fix ignoring LIMIT offset

"SELECT DISTINCT col FROM table LIMIT O,N" should skip first O rows
---
 dbcon/joblist/tupleannexstep.cpp | 25 ++++++++++++++++---------
 1 file changed, 16 insertions(+), 9 deletions(-)

diff --git a/dbcon/joblist/tupleannexstep.cpp b/dbcon/joblist/tupleannexstep.cpp
index 6861681a5..cca0977ba 100644
--- a/dbcon/joblist/tupleannexstep.cpp
+++ b/dbcon/joblist/tupleannexstep.cpp
@@ -513,26 +513,31 @@ void TupleAnnexStep::executeNoOrderByWithDistinct()
             {
                 pair<DistinctMap_t::iterator, bool> inserted;
 
-                if (fConstant)
-                    fConstant->fillInConstants(fRowIn, fRowOut);
-                else
-                    copyRow(fRowIn, &fRowOut);
-
+                inserted = distinctMap->insert(fRowIn.getPointer());
                 ++fRowsProcessed;
-                fRowIn.nextRow();
-
-                inserted = distinctMap->insert(fRowOut.getPointer());
 
                 if (inserted.second)
                 {
+                    // skip first limit-start rows
+                    if (distinctMap->size() <= fLimitStart)
+                    {
+                        fRowIn.nextRow();
+                        continue;
+                    }
+
                     if (UNLIKELY(fRowsReturned >= fLimitCount))
                     {
                         fLimitHit = true;
                         fJobList->abortOnLimit((JobStep*) this);
-                        continue;
+                        break;
                     }
 
                     ++fRowsReturned;
+                    if (fConstant)
+                        fConstant->fillInConstants(fRowIn, fRowOut);
+                    else
+                        copyRow(fRowIn, &fRowOut);
+
                     fRowGroupOut.incRowCount();
                     fRowOut.nextRow();
 
@@ -545,6 +550,8 @@ void TupleAnnexStep::executeNoOrderByWithDistinct()
                         fRowGroupOut.getRow(0, &fRowOut);
                     }
                 }
+
+                fRowIn.nextRow();
             }
 
             more = fInputDL->next(fInputIterator, &rgDataIn);