Fixed that LEFT OUTER JOIN was replaced with a regulat join

in some cases, because "charset(x) = 'string'" was considered
as "x is not null" due to incorrect not_null_tables().

mysql-test/r/func_str.result

@@ -636,6 +636,26 @@ drop table t1;
 select charset(null), collation(null), coercibility(null);
 charset(null)	collation(null)	coercibility(null)
 binary	binary	5
+CREATE TABLE t1 (a int, b int);
+CREATE TABLE t2 (a int, b int);
+INSERT INTO t1 VALUES (1,1),(2,2);
+INSERT INTO t2 VALUES (2,2),(3,3);
+select t1.*,t2.* from t1 left join t2 on (t1.b=t2.b)
+where collation(t2.a) = _utf8'binary' order by t1.a,t2.a;
+a	b	a	b
+1	1	NULL	NULL
+2	2	2	2
+select t1.*,t2.* from t1 left join t2 on (t1.b=t2.b)
+where charset(t2.a) = _utf8'binary' order by t1.a,t2.a;
+a	b	a	b
+1	1	NULL	NULL
+2	2	2	2
+select t1.*,t2.* from t1 left join t2 on (t1.b=t2.b)
+where coercibility(t2.a) = 2 order by t1.a,t2.a;
+a	b	a	b
+1	1	NULL	NULL
+2	2	2	2
+DROP TABLE t1, t2;
 select SUBSTR('abcdefg',3,2);
 SUBSTR('abcdefg',3,2)
 cd

mysql-test/t/func_str.test

@@ -376,6 +376,20 @@ insert into t1 values (null);
 select charset(a), collation(a), coercibility(a) from t1;
 drop table t1;
 select charset(null), collation(null), coercibility(null);
+#
+# Make sure OUTER JOIN is not replaced with a regular joun
+#
+CREATE TABLE t1 (a int, b int);
+CREATE TABLE t2 (a int, b int);
+INSERT INTO t1 VALUES (1,1),(2,2);
+INSERT INTO t2 VALUES (2,2),(3,3);
+select t1.*,t2.* from t1 left join t2 on (t1.b=t2.b)
+where collation(t2.a) = _utf8'binary' order by t1.a,t2.a;
+select t1.*,t2.* from t1 left join t2 on (t1.b=t2.b)
+where charset(t2.a) = _utf8'binary' order by t1.a,t2.a;
+select t1.*,t2.* from t1 left join t2 on (t1.b=t2.b)
+where coercibility(t2.a) = 2 order by t1.a,t2.a;
+DROP TABLE t1, t2;
 
 #
 # test for SUBSTR

sql/item_func.h

@@ -616,7 +616,8 @@ class Item_func_coercibility :public Item_int_func
   Item_func_coercibility(Item *a) :Item_int_func(a) {}
   longlong val_int();
   const char *func_name() const { return "coercibility"; }
-  void fix_length_and_dec() { max_length=10; }
+  void fix_length_and_dec() { max_length=10; maybe_null= 0; }
+  table_map not_null_tables() const { return 0; }
 };
 
 class Item_func_locate :public Item_int_func

sql/item_strfunc.h

@@ -641,7 +641,9 @@ class Item_func_charset :public Item_str_func
   {
      collation.set(system_charset_info);
      max_length= 64 * collation.collation->mbmaxlen; // should be enough
+     maybe_null= 0;
   };
+  table_map not_null_tables() const { return 0; }
 };
 
 class Item_func_collation :public Item_str_func
@@ -654,7 +656,9 @@ class Item_func_collation :public Item_str_func
   {
      collation.set(system_charset_info);
      max_length= 64 * collation.collation->mbmaxlen; // should be enough
+     maybe_null= 0;
   };
+  table_map not_null_tables() const { return 0; }
 };
 
 class Item_func_crc32 :public Item_int_func