From db4735a10508e02b50565bba8a1e71161df90f82 Mon Sep 17 00:00:00 2001
From: Yarik Briukhovetskyi <114298166+yariks5s@users.noreply.github.com>
Date: Mon, 17 Jul 2023 12:12:25 +0000
Subject: [PATCH] Implemented requested changes

---
 src/Functions/array/arrayIntersect.cpp | 47 +++++++++++---------------
 1 file changed, 20 insertions(+), 27 deletions(-)

diff --git a/src/Functions/array/arrayIntersect.cpp b/src/Functions/array/arrayIntersect.cpp
index 7a8bde7ab5f..83b26b56071 100644
--- a/src/Functions/array/arrayIntersect.cpp
+++ b/src/Functions/array/arrayIntersect.cpp
@@ -510,7 +510,7 @@ ColumnPtr FunctionArrayIntersect::execute(const UnpackedArrays & arrays, Mutable
         map.clear();
 
         bool all_has_nullable = all_nullable;
-        bool current_has_nullable = false;
+        bool current_has_nullable;
 
         for (size_t arg_num = 0; arg_num < args; ++arg_num)
         {
@@ -549,7 +549,8 @@ ColumnPtr FunctionArrayIntersect::execute(const UnpackedArrays & arrays, Mutable
                         ++(*value);
                 }
             }
-
+            // We update offsets for all the arrays except the first one. Offsets for the first array would be updated later. 
+            // It is needed to iterate the first array again so that the elements in the result would have fixed order.
             if (arg_num)
             {
                 prev_off[arg_num] = off;
@@ -570,15 +571,21 @@ ColumnPtr FunctionArrayIntersect::execute(const UnpackedArrays & arrays, Mutable
         else
             off = (*arg.offsets)[row];
 
+        bool is_map_serialized = false;
         for (auto i : collections::range(prev_off[0], off))
         {
-            all_has_nullable = all_nullable;
-            current_has_nullable = false;
             typename Map::LookupResult pair = nullptr;
 
             if (arg.null_map && (*arg.null_map)[i])
             {
                 current_has_nullable = true;
+                if (all_has_nullable && !null_added)
+                {
+                    ++result_offset;
+                    result_data.insertDefault();
+                    null_map.push_back(1);
+                    null_added = true;
+                }
                 if (null_added)
                     continue;
             }
@@ -591,51 +598,37 @@ ColumnPtr FunctionArrayIntersect::execute(const UnpackedArrays & arrays, Mutable
             else
             {
                 const char * data = nullptr;
-                pair = map.find(columns[0]->serializeValueIntoArena(i, arena, data));
+                if (!is_map_serialized)
+                {
+                    pair = map.find(columns[0]->serializeValueIntoArena(i, arena, data));
+                    is_map_serialized = true;
+                }
             }
             prev_off[0] = off;
             if (arg.is_const)
                 prev_off[0] = 0;
 
-            if (!current_has_nullable)
-                all_has_nullable = false;
-
             if (pair && pair->getMapped() == args)
             {
+                // We increase pair->getMapped() here to not skip duplicate values from the first array.
                 ++pair->getMapped();
                 ++result_offset;
                 if constexpr (is_numeric_column)
                 {
-                    if (pair->getKey() == columns[0]->getElement(i))
-                    {
-                        result_data.insertValue(pair->getKey());
-                    }
+                    result_data.insertValue(pair->getKey());
                 }
                 else if constexpr (std::is_same_v<ColumnType, ColumnString> || std::is_same_v<ColumnType, ColumnFixedString>)
                 {
-                    if (pair->getKey() == columns[0]->getDataAt(i))
-                    {
-                        result_data.insertData(pair->getKey().data, pair->getKey().size);
-                    }
+                    result_data.insertData(pair->getKey().data, pair->getKey().size);
                 }
                 else
                 {
                     const char * data = nullptr;
-                    if (pair->getKey() == columns[0]->serializeValueIntoArena(i, arena, data))
-                    {
-                        result_data.deserializeAndInsertFromArena(pair->getKey().data);
-                    }
+                    result_data.deserializeAndInsertFromArena(pair->getKey().data);
                 }
                 if (all_nullable)
                     null_map.push_back(0);
             }
-            if (all_has_nullable && !null_added)
-            {
-                ++result_offset;
-                result_data.insertDefault();
-                null_map.push_back(1);
-                null_added = true;
-            }
         }
         result_offsets.getElement(row) = result_offset;