MDEV-8785 Wrong results for EXPLAIN EXTENDED...WHERE NULLIF(latin1_col, _utf8'a' COLLATE utf8_bin) IS NOT NULL

4 files changed, 57 insertions, 0 deletions

diff --git a/mysql-test/r/explain_json.result b/mysql-test/r/explain_json.result
index d741c1e5362..07ff72b4208 100644
--- a/mysql-test/r/explain_json.result
+++ b/mysql-test/r/explain_json.result
@@ -1090,3 +1090,23 @@ EXPLAIN
   }
 }
 DROP TABLE t1;
+#
+# MDEV-8785 Wrong results for EXPLAIN EXTENDED...WHERE NULLIF(latin1_col, _utf8'a' COLLATE utf8_bin) IS NOT NULL
+#
+CREATE TABLE t1 (a VARCHAR(10) CHARACTER SET latin1);
+INSERT INTO t1 VALUES ('a'),('A');
+EXPLAIN FORMAT=JSON SELECT * FROM t1 WHERE NULLIF(a,_utf8'a' COLLATE utf8_bin);
+EXPLAIN
+{
+  "query_block": {
+    "select_id": 1,
+    "table": {
+      "table_name": "t1",
+      "access_type": "ALL",
+      "rows": 2,
+      "filtered": 100,
+      "attached_condition": "(case when convert(t1.a using utf8) = <cache>((_utf8'a' collate utf8_bin)) then NULL else t1.a end)"
+    }
+  }
+}
+DROP TABLE t1;
diff --git a/mysql-test/r/null.result b/mysql-test/r/null.result
index debb3c05681..e5ce6a10f09 100644
--- a/mysql-test/r/null.result
+++ b/mysql-test/r/null.result
@@ -1390,5 +1390,24 @@ Warning	1292	Incorrect datetime value: '1'
 Warning	1292	Incorrect datetime value: '1'
 DROP TABLE t1;
 #
+# MDEV-8785 Wrong results for EXPLAIN EXTENDED...WHERE NULLIF(latin1_col, _utf8'a' COLLATE utf8_bin) IS NOT NULL
+#
+CREATE TABLE t1 (a VARCHAR(10) CHARACTER SET latin1);
+INSERT INTO t1 VALUES ('a'),('A');
+SELECT a, NULLIF(a,_utf8'a' COLLATE utf8_bin) IS NULL FROM t1;
+a	NULLIF(a,_utf8'a' COLLATE utf8_bin) IS NULL
+a	1
+A	0
+SELECT CHARSET(NULLIF(a,_utf8'a' COLLATE utf8_bin)) FROM t1;
+CHARSET(NULLIF(a,_utf8'a' COLLATE utf8_bin))
+latin1
+latin1
+EXPLAIN EXTENDED SELECT NULLIF(a,_utf8'a' COLLATE utf8_bin) IS NULL AS expr FROM t1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	2	100.00	
+Warnings:
+Note	1003	select isnull((case when convert(`test`.`t1`.`a` using utf8) = (_utf8'a' collate utf8_bin) then NULL else `test`.`t1`.`a` end)) AS `expr` from `test`.`t1`
+DROP TABLE t1;
+#
 # End of 10.1 tests
 #
diff --git a/mysql-test/t/explain_json.test b/mysql-test/t/explain_json.test
index e12cbed6d52..1078222725e 100644
--- a/mysql-test/t/explain_json.test
+++ b/mysql-test/t/explain_json.test
@@ -286,3 +286,11 @@ CREATE TABLE t1 (a VARCHAR(10) CHARACTER SET latin1);
 INSERT INTO t1 VALUES ('a'),('b');
 EXPLAIN FORMAT=JSON SELECT * FROM t1 WHERE a=_latin1 0xDF;
 DROP TABLE t1;
+
+--echo #
+--echo # MDEV-8785 Wrong results for EXPLAIN EXTENDED...WHERE NULLIF(latin1_col, _utf8'a' COLLATE utf8_bin) IS NOT NULL
+--echo #
+CREATE TABLE t1 (a VARCHAR(10) CHARACTER SET latin1);
+INSERT INTO t1 VALUES ('a'),('A');
+EXPLAIN FORMAT=JSON SELECT * FROM t1 WHERE NULLIF(a,_utf8'a' COLLATE utf8_bin);
+DROP TABLE t1;
diff --git a/mysql-test/t/null.test b/mysql-test/t/null.test
index 65a45b9a21c..695c22f3bbd 100644
--- a/mysql-test/t/null.test
+++ b/mysql-test/t/null.test
@@ -868,6 +868,16 @@ CREATE TABLE t1 AS SELECT
   END AS b;
 DROP TABLE t1;
 
+--echo #
+--echo # MDEV-8785 Wrong results for EXPLAIN EXTENDED...WHERE NULLIF(latin1_col, _utf8'a' COLLATE utf8_bin) IS NOT NULL
+--echo #
+CREATE TABLE t1 (a VARCHAR(10) CHARACTER SET latin1);
+INSERT INTO t1 VALUES ('a'),('A');
+SELECT a, NULLIF(a,_utf8'a' COLLATE utf8_bin) IS NULL FROM t1;
+SELECT CHARSET(NULLIF(a,_utf8'a' COLLATE utf8_bin)) FROM t1;
+EXPLAIN EXTENDED SELECT NULLIF(a,_utf8'a' COLLATE utf8_bin) IS NULL AS expr FROM t1;
+DROP TABLE t1;
+
 
 --echo #
 --echo # End of 10.1 tests