From 2e404c98507740ebffcb23cfbf35d10c62916af5 Mon Sep 17 00:00:00 2001
From: Alexander Barkov <bar@mariadb.com>
Date: Tue, 12 Nov 2024 11:06:32 +0400
Subject: [PATCH] MDEV-21029 Incorrect result for expression with the <=>
 operator and IS NULL

Item_func_equal erroneously derived is_null() from the parent class.
Overriding it to return false because <=> can never return NULL.
---
 mysql-test/main/func_equal.result | 11 +++++++++++
 mysql-test/main/func_equal.test   | 15 +++++++++++++++
 sql/item_cmpfunc.h                |  1 +
 3 files changed, 27 insertions(+)

diff --git a/mysql-test/main/func_equal.result b/mysql-test/main/func_equal.result
index f20b259191c..4f876b4f27b 100644
--- a/mysql-test/main/func_equal.result
+++ b/mysql-test/main/func_equal.result
@@ -43,3 +43,14 @@ a
 4828532208463511553
 drop table t1;
 #End of 4.1 tests
+# Start of 10.5 tests
+#
+# MDEV-21029 Incorrect result for expression with the <=> operator and IS NULL
+#
+CREATE TABLE t0(c0 INT);
+INSERT INTO t0 VALUES (1);
+SELECT (c0 > (NULL <=> 0)) IS NULL AS c1 FROM t0;
+c1
+0
+DROP TABLE t0;
+# End of 10.5 tests
diff --git a/mysql-test/main/func_equal.test b/mysql-test/main/func_equal.test
index f17ebb5bd84..88cab9e95a0 100644
--- a/mysql-test/main/func_equal.test
+++ b/mysql-test/main/func_equal.test
@@ -44,3 +44,18 @@ select * from t1 where a in ('4828532208463511553');
 drop table t1;
 
 --echo #End of 4.1 tests
+
+
+--echo # Start of 10.5 tests
+
+--echo #
+--echo # MDEV-21029 Incorrect result for expression with the <=> operator and IS NULL
+--echo #
+
+CREATE TABLE t0(c0 INT);
+INSERT INTO t0 VALUES (1);
+SELECT (c0 > (NULL <=> 0)) IS NULL AS c1 FROM t0;
+DROP TABLE t0;
+
+
+--echo # End of 10.5 tests
diff --git a/sql/item_cmpfunc.h b/sql/item_cmpfunc.h
index 1bc5f42ab2b..3d15a6f3dc1 100644
--- a/sql/item_cmpfunc.h
+++ b/sql/item_cmpfunc.h
@@ -782,6 +782,7 @@ public:
   enum Functype functype() const override { return EQUAL_FUNC; }
   enum Functype rev_functype() const override { return EQUAL_FUNC; }
   cond_result eq_cmp_result() const override { return COND_TRUE; }
+  bool is_null() override { return false; }
   const char *func_name() const override { return "<=>"; }
   Item *neg_transformer(THD *thd) override { return 0; }
   void add_key_fields(JOIN *join, KEY_FIELD **key_fields,