From 0ad593404dc23c511f2e8a0b8a550f9f3e70c0ff Mon Sep 17 00:00:00 2001
From: fuzhe1989 <fuzhe1989@gmail.com>
Date: Fri, 5 Nov 2021 17:41:59 +0800
Subject: [PATCH 1/2] update

---
 dbms/src/Functions/FunctionsNull.cpp          |  2 +-
 dbms/src/Functions/tests/gtest_coalesce.cpp   | 34 +++++++++++++++++++
 .../expr/coalesce_pushdown.test               | 16 +++++++--
 3 files changed, 48 insertions(+), 4 deletions(-)
 create mode 100644 dbms/src/Functions/tests/gtest_coalesce.cpp

diff --git a/dbms/src/Functions/FunctionsNull.cpp b/dbms/src/Functions/FunctionsNull.cpp
index 84b13497a75..61f7bb6ec2f 100644
--- a/dbms/src/Functions/FunctionsNull.cpp
+++ b/dbms/src/Functions/FunctionsNull.cpp
@@ -213,7 +213,7 @@ void FunctionCoalesce::executeImpl(Block & block, const ColumnNumbers & argument
     ColumnPtr res = std::move(temp_block.getByPosition(result).column);
 
     /// if last argument is not nullable, result should be also not nullable
-    if (!block.getByPosition(multi_if_args.back()).column->isColumnNullable() && res->isColumnNullable())
+    if (!block.getByPosition(filtered_args.back()).type->isNullable() && res->isColumnNullable())
         res = static_cast<const ColumnNullable &>(*res).getNestedColumnPtr();
 
     block.getByPosition(result).column = std::move(res);
diff --git a/dbms/src/Functions/tests/gtest_coalesce.cpp b/dbms/src/Functions/tests/gtest_coalesce.cpp
new file mode 100644
index 00000000000..5d338e65c1f
--- /dev/null
+++ b/dbms/src/Functions/tests/gtest_coalesce.cpp
@@ -0,0 +1,34 @@
+#include <Interpreters/Context.h>
+#include <TestUtils/FunctionTestUtils.h>
+#include <TestUtils/TiFlashTestBasic.h>
+
+#include <string>
+#include <vector>
+
+namespace DB::tests
+{
+class CoalesceTest : public DB::tests::FunctionTest
+{
+};
+
+TEST_F(CoalesceTest, testOnlyNull)
+try
+{
+    const String & func_name = "coalesce";
+
+    ASSERT_COLUMN_EQ(
+        createColumn<Nullable<String>>({"a"}),
+        executeFunction(
+            func_name,
+            createColumn<Nullable<String>>({"a"}),
+            createConstColumn<Nullable<String>>(1, std::nullopt)));
+
+    ASSERT_COLUMN_EQ(
+        createColumn<Nullable<String>>({"a"}),
+        executeFunction(
+            func_name,
+            createColumn<Nullable<String>>({"a"}),
+            createOnlyNullColumn(1)));
+}
+CATCH
+} // namespace DB::tests
diff --git a/tests/fullstack-test/expr/coalesce_pushdown.test b/tests/fullstack-test/expr/coalesce_pushdown.test
index 9b89f5e76d8..e10c281a847 100644
--- a/tests/fullstack-test/expr/coalesce_pushdown.test
+++ b/tests/fullstack-test/expr/coalesce_pushdown.test
@@ -5,9 +5,11 @@ mysql> INSERT INTO test.test_tb(id,char_,enum_,longtext_,mediumtext_,set_,text_,
 
 mysql> analyze table test.test_tb
 mysql> alter table test.test_tb set tiflash replica 1
-func> wait_table test test_tb
-
-
+mysql> drop table if exists test.fix_3388
+mysql> create table if not exists test.fix_3388(a varchar(10))
+mysql> alter table test.fix_3388 set tiflash replica 1
+mysql> insert into test.fix_3388 values ("a")
+func> wait_table test test_tb fix_3388
 
 # start checking
 mysql> select /*+ read_from_storage(tiflash[test.test_tb]) */ id from test.test_tb where char_ = coalesce(null, char_);
@@ -335,3 +337,11 @@ mysql> select /*+ read_from_storage(tiflash[test.test_tb]) */ id from test.test_
 |  2 |
 +----+
 
+# fix 3388
+mysql> set tidb_enforce_mpp=1; select count(*) from test.fix_3388 where coalesce(a, null) = "a"
++----------+
+| count(*) |
++----------+
+|        1 |
++----------+
+

From d2611a53bbbdcd631c6bd615bd58a74f645b0a3c Mon Sep 17 00:00:00 2001
From: Fu Zhe <fuzhe1989@gmail.com>
Date: Fri, 5 Nov 2021 19:29:09 +0800
Subject: [PATCH 2/2] Update coalesce_pushdown.test

---
 tests/fullstack-test/expr/coalesce_pushdown.test | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tests/fullstack-test/expr/coalesce_pushdown.test b/tests/fullstack-test/expr/coalesce_pushdown.test
index e10c281a847..698de84e350 100644
--- a/tests/fullstack-test/expr/coalesce_pushdown.test
+++ b/tests/fullstack-test/expr/coalesce_pushdown.test
@@ -8,7 +8,7 @@ mysql> alter table test.test_tb set tiflash replica 1
 mysql> drop table if exists test.fix_3388
 mysql> create table if not exists test.fix_3388(a varchar(10))
 mysql> alter table test.fix_3388 set tiflash replica 1
-mysql> insert into test.fix_3388 values ("a")
+mysql> insert into test.fix_3388 values ('a')
 func> wait_table test test_tb fix_3388
 
 # start checking