MDEV-6993 Bad results with join comparing DECIMAL and ENUM/SET columns

mysql-test/r/type_enum.result

@@ -2046,5 +2046,39 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t1	index	NULL	id	6	NULL	16	Using where; Using index
 DROP TABLE t1;
 #
+# MDEV-6993 Bad results with join comparing DECIMAL and ENUM/SET columns
+#
+CREATE TABLE t1 (c1 DECIMAL(10,1) PRIMARY KEY);
+INSERT INTO t1 VALUES (1),(2);
+CREATE TABLE t2 (c1 ENUM('a','b'));
+INSERT INTO t2 VALUES ('a'),('b');
+SELECT t1.* FROM t1 NATURAL JOIN t2;
+c1
+1.0
+2.0
+ALTER TABLE t2 ADD PRIMARY KEY(c1);
+SELECT t1.* FROM t1 NATURAL JOIN t2;
+c1
+1.0
+2.0
+SELECT t1.* FROM t1 LEFT OUTER JOIN t2 USING (c1);
+c1
+1.0
+2.0
+DROP TABLE t1,t2;
+CREATE TABLE t1 (a DECIMAL(10,1), b ENUM('1','2'));
+INSERT INTO t1 (a) VALUES (1),(2);
+UPDATE t1 SET b=a;
+SELECT * FROM t1;
+a	b
+1.0	1
+2.0	2
+ALTER TABLE t1 MODIFY a ENUM('1','2');
+SELECT * FROM t1;
+a	b
+1	1
+2	2
+DROP TABLE t1;
+#
 # End of 10.0 tests
 #

mysql-test/r/type_set.result

@@ -227,5 +227,39 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t2	index	PRIMARY	PRIMARY	1	NULL	2	Using where; Using index
 DROP TABLE IF EXISTS t1,t2;
 #
+# MDEV-6993 Bad results with join comparing DECIMAL and ENUM/SET columns
+#
+CREATE TABLE t1 (c1 DECIMAL(10,1) PRIMARY KEY);
+INSERT INTO t1 VALUES (1),(2);
+CREATE TABLE t2 (c1 SET('a','b'));
+INSERT INTO t2 VALUES ('a'),('b');
+SELECT t1.* FROM t1 NATURAL JOIN t2;
+c1
+1.0
+2.0
+ALTER TABLE t2 ADD PRIMARY KEY(c1);
+SELECT t1.* FROM t1 NATURAL JOIN t2;
+c1
+1.0
+2.0
+SELECT t1.* FROM t1 LEFT OUTER JOIN t2 USING (c1);
+c1
+1.0
+2.0
+DROP TABLE t1,t2;
+CREATE TABLE t1 (a DECIMAL(10,1), b SET('1','2'));
+INSERT INTO t1 (a) VALUES (1),(2);
+UPDATE t1 SET b=a;
+SELECT * FROM t1;
+a	b
+1.0	1
+2.0	2
+ALTER TABLE t1 MODIFY a SET('1','2');
+SELECT * FROM t1;
+a	b
+1	1
+2	2
+DROP TABLE t1;
+#
 # End of 10.0 tests
 #

mysql-test/t/type_enum.test

@@ -333,6 +333,27 @@ SELECT id,MIN(a),MAX(a) FROM t1 WHERE a<=3 GROUP BY id;
 EXPLAIN SELECT id,MIN(a),MAX(a) FROM t1 WHERE a<=3 GROUP BY id;
 DROP TABLE t1;
 
+--echo #
+--echo # MDEV-6993 Bad results with join comparing DECIMAL and ENUM/SET columns
+--echo #
+CREATE TABLE t1 (c1 DECIMAL(10,1) PRIMARY KEY);
+INSERT INTO t1 VALUES (1),(2);
+CREATE TABLE t2 (c1 ENUM('a','b'));
+INSERT INTO t2 VALUES ('a'),('b');
+SELECT t1.* FROM t1 NATURAL JOIN t2;
+ALTER TABLE t2 ADD PRIMARY KEY(c1);
+SELECT t1.* FROM t1 NATURAL JOIN t2;
+SELECT t1.* FROM t1 LEFT OUTER JOIN t2 USING (c1);
+DROP TABLE t1,t2;
+
+CREATE TABLE t1 (a DECIMAL(10,1), b ENUM('1','2'));
+INSERT INTO t1 (a) VALUES (1),(2);
+UPDATE t1 SET b=a;
+SELECT * FROM t1;
+ALTER TABLE t1 MODIFY a ENUM('1','2');
+SELECT * FROM t1;
+DROP TABLE t1;
+
 --echo #
 --echo # End of 10.0 tests
 --echo #

mysql-test/t/type_set.test

@@ -161,6 +161,27 @@ SELECT t1.* FROM t1 LEFT JOIN t2 ON t1.c1 COLLATE latin1_swedish_ci=t2.c1;
 EXPLAIN SELECT t1.* FROM t1 LEFT JOIN t2 ON t1.c1 COLLATE latin1_swedish_ci=t2.c1;
 DROP TABLE IF EXISTS t1,t2;
 
+--echo #
+--echo # MDEV-6993 Bad results with join comparing DECIMAL and ENUM/SET columns
+--echo #
+CREATE TABLE t1 (c1 DECIMAL(10,1) PRIMARY KEY);
+INSERT INTO t1 VALUES (1),(2);
+CREATE TABLE t2 (c1 SET('a','b'));
+INSERT INTO t2 VALUES ('a'),('b');
+SELECT t1.* FROM t1 NATURAL JOIN t2;
+ALTER TABLE t2 ADD PRIMARY KEY(c1);
+SELECT t1.* FROM t1 NATURAL JOIN t2;
+SELECT t1.* FROM t1 LEFT OUTER JOIN t2 USING (c1);
+DROP TABLE t1,t2;
+
+CREATE TABLE t1 (a DECIMAL(10,1), b SET('1','2'));
+INSERT INTO t1 (a) VALUES (1),(2);
+UPDATE t1 SET b=a;
+SELECT * FROM t1;
+ALTER TABLE t1 MODIFY a SET('1','2');
+SELECT * FROM t1;
+DROP TABLE t1;
+
 --echo #
 --echo # End of 10.0 tests
 --echo #

sql/field_conv.cc

@@ -792,6 +792,10 @@ Copy_field::get_copy_func(Field *to,Field *from)
     else if (to->real_type() != from->real_type() ||
 	     to_length != from_length)
     {
+      if ((to->real_type() == MYSQL_TYPE_ENUM ||
+           to->real_type() == MYSQL_TYPE_SET) &&
+          from->real_type() == MYSQL_TYPE_NEWDECIMAL)
+        return do_field_decimal;
       if (to->real_type() == MYSQL_TYPE_DECIMAL ||
 	  to->result_type() == STRING_RESULT)
 	return do_field_string;