MDEV-8688 Wrong result for

          SELECT..WHERE varchar_column IN (1,2,3) AND varchar_column=' 1';

mysql-test/r/ctype_cp1251.result

@@ -3334,3 +3334,34 @@ DROP TABLE t1;
 #
 # End of 5.5 tests
 #
+#
+# Start of 10.1 tests
+#
+#
+# MDEV-8688 Wrong result for SELECT..WHERE varchar_column IN (1,2,3) AND varchar_column=' 1';
+#
+CREATE TABLE t1 (a VARCHAR(10) CHARACTER SET cp1251 COLLATE cp1251_ukrainian_ci);
+INSERT INTO t1 VALUES (' 1'),('`1');
+SELECT * FROM t1 WHERE a IN (1,2,3);
+a
+ 1
+SELECT * FROM t1 WHERE a IN (1,2,3) AND a=' 1';
+a
+ 1
+SELECT * FROM t1 WHERE a IN (1,2,3,'4') AND a=' 1';
+a
+ 1
+EXPLAIN EXTENDED SELECT * FROM t1 WHERE a IN (1,2,3) AND a=' 1';
+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	Using where
+Warnings:
+Note	1003	select `test`.`t1`.`a` AS `a` from `test`.`t1` where ((`test`.`t1`.`a` = ' 1') and (`test`.`t1`.`a` in (1,2,3)))
+EXPLAIN EXTENDED SELECT * FROM t1 WHERE a IN (1,2,3,'x') AND a=' 1';
+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	Using where
+Warnings:
+Note	1003	select `test`.`t1`.`a` AS `a` from `test`.`t1` where ((`test`.`t1`.`a` = ' 1') and (`test`.`t1`.`a` in (1,2,3,'x')))
+DROP TABLE t1;
+#
+# End of 10.1 tests
+#

mysql-test/r/ctype_utf8.result

@@ -10166,5 +10166,31 @@ Warnings:
 Note	1003	select `test`.`t1`.`a` AS `a` from `test`.`t1` where ((`test`.`t1`.`a` = 10) and (`test`.`t1`.`a` = '1e1'))
 DROP TABLE t1;
 #
+# MDEV-8688 Wrong result for SELECT..WHERE varchar_column IN (1,2,3) AND varchar_column=' 1';
+#
+SET NAMES utf8;
+CREATE TABLE t1 (a VARCHAR(10) CHARACTER SET latin1);
+INSERT INTO t1 VALUES ('1e1'),('1ë1');
+SELECT * FROM t1 WHERE a IN (1,2);
+a
+1ë1
+SELECT * FROM t1 WHERE a IN (1,2) AND a='1ë1';
+a
+1ë1
+SELECT * FROM t1 WHERE a IN (1,2,'x') AND a='1ë1';
+a
+1ë1
+EXPLAIN EXTENDED SELECT * FROM t1 WHERE a IN (1,2) AND a='1ë1';
+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	Using where
+Warnings:
+Note	1003	select `test`.`t1`.`a` AS `a` from `test`.`t1` where ((`test`.`t1`.`a` = '1ë1') and (`test`.`t1`.`a` in (1,2)))
+EXPLAIN EXTENDED SELECT * FROM t1 WHERE a IN (1,2,'x') AND a='1ë1';
+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	Using where
+Warnings:
+Note	1003	select `test`.`t1`.`a` AS `a` from `test`.`t1` where ((`test`.`t1`.`a` = '1ë1') and (`test`.`t1`.`a` in (1,2,'x')))
+DROP TABLE IF EXISTS t1;
+#
 # End of 10.1 tests
 #

mysql-test/t/ctype_cp1251.test

@@ -107,3 +107,25 @@ DROP TABLE t1;
 --echo #
 --echo # End of 5.5 tests
 --echo #
+
+--echo #
+--echo # Start of 10.1 tests
+--echo #
+
+--echo #
+--echo # MDEV-8688 Wrong result for SELECT..WHERE varchar_column IN (1,2,3) AND varchar_column=' 1';
+--echo #
+CREATE TABLE t1 (a VARCHAR(10) CHARACTER SET cp1251 COLLATE cp1251_ukrainian_ci);
+INSERT INTO t1 VALUES (' 1'),('`1');
+SELECT * FROM t1 WHERE a IN (1,2,3);
+SELECT * FROM t1 WHERE a IN (1,2,3) AND a=' 1';
+SELECT * FROM t1 WHERE a IN (1,2,3,'4') AND a=' 1';
+# Equality should not propagate ' 1' to IN: incompatible comparison context
+EXPLAIN EXTENDED SELECT * FROM t1 WHERE a IN (1,2,3) AND a=' 1';
+EXPLAIN EXTENDED SELECT * FROM t1 WHERE a IN (1,2,3,'x') AND a=' 1';
+DROP TABLE t1;
+
+
+--echo #
+--echo # End of 10.1 tests
+--echo #

mysql-test/t/ctype_utf8.test

@@ -1818,6 +1818,20 @@ SELECT * FROM t1 WHERE (a,a)=(10,'1e1');
 EXPLAIN EXTENDED SELECT * FROM t1 WHERE (a,a)=(10,'1e1');
 DROP TABLE t1;
 
+--echo #
+--echo # MDEV-8688 Wrong result for SELECT..WHERE varchar_column IN (1,2,3) AND varchar_column=' 1';
+--echo #
+SET NAMES utf8;
+CREATE TABLE t1 (a VARCHAR(10) CHARACTER SET latin1);
+INSERT INTO t1 VALUES ('1e1'),('1ë1');
+SELECT * FROM t1 WHERE a IN (1,2);
+SELECT * FROM t1 WHERE a IN (1,2) AND a='1ë1';
+SELECT * FROM t1 WHERE a IN (1,2,'x') AND a='1ë1';
+# Equality should not propagate '1ë1' to IN: incompatible comparison context
+EXPLAIN EXTENDED SELECT * FROM t1 WHERE a IN (1,2) AND a='1ë1';
+EXPLAIN EXTENDED SELECT * FROM t1 WHERE a IN (1,2,'x') AND a='1ë1';
+DROP TABLE IF EXISTS t1;
+
 
 --echo #
 --echo # End of 10.1 tests

sql/item_cmpfunc.cc

@@ -3999,6 +3999,7 @@ void Item_func_in::fix_length_and_dec()
     if (m_compare_type == STRING_RESULT &&
         agg_arg_charsets_for_comparison(cmp_collation, args, arg_count))
       return;
+    args[0]->cmp_context= m_compare_type;
     arg_types_compatible= TRUE;
 
     if (m_compare_type == ROW_RESULT)

sql/item_cmpfunc.h

@@ -1392,6 +1392,20 @@ public:
   void add_key_fields(JOIN *join, KEY_FIELD **key_fields, uint *and_level,
                       table_map usable_tables, SARGABLE_PARAM **sargables);
   SEL_TREE *get_mm_tree(RANGE_OPT_PARAM *param, Item **cond_ptr);
+  Item* propagate_equal_fields(THD *thd, const Context &ctx, COND_EQUAL *cond)
+  {
+    /*
+      In case when arg_types_compatible is false,
+      fix_length_and_dec() leaves args[0]->cmp_context equal to
+      IMPOSSIBLE_CONTEXT. In this case it's not safe to replace the field to an
+      equal constant, because Item_field::can_be_substituted_to_equal_item()
+      won't be able to check compatibility between
+      Item_equal->compare_collation() and this->compare_collation().
+    */
+    return arg_types_compatible ?
+           Item_func_opt_neg::propagate_equal_fields(thd, ctx, cond) :
+           this;
+  }
   virtual void print(String *str, enum_query_type query_type);
   enum Functype functype() const { return IN_FUNC; }
   const char *func_name() const { return " IN "; }