Fix for LP BUG#944504

Problem is that subquery execution can't be called during prepare/optimize phase.

Also small fix for subquery test suite.

mysql-test/r/ctype_recoding.result

@@ -267,3 +267,19 @@ drop table t1;
 create table t1(a char character set latin1 default _cp1251 0xFF);
 ERROR 42000: Invalid default value for 'a'
 End of 4.1 tests
+SET CHARACTER SET DEFAULT;
+#
+# LP BUG#944504 Item_func_conv_charset tries to execute subquery constant
+# 
+SET optimizer_switch = 'in_to_exists=on';
+SET character_set_connection = utf8;
+CREATE TABLE t1 ( a VARCHAR(1) );
+INSERT INTO t1 VALUES ('m'),('n');
+CREATE VIEW v1 AS SELECT 'w' ;
+SELECT * FROM t1 WHERE a < ALL ( SELECT * FROM v1 );
+ERROR HY000: Illegal mix of collations (utf8_general_ci,COERCIBLE) and (latin1_swedish_ci,IMPLICIT) for operation '<='
+drop view v1;
+drop table t1;
+SET character_set_connection = default;
+SET optimizer_switch= default;
+#End of 5.3 tests

mysql-test/r/subselect.result

@@ -5994,6 +5994,7 @@ SELECT ( SELECT b FROM t2 WHERE b = a OR rand() * 0) FROM t1;
 1
 NULL
 drop table t1,t2,t3;
+set optimizer_switch=@subselect_tmp;
 #
 # LP BUG#905353 Wrong non-empty result with a constant table,
 # aggregate function in subquery, MyISAM or Aria

mysql-test/r/subselect_no_mat.result

@@ -5993,6 +5993,7 @@ SELECT ( SELECT b FROM t2 WHERE b = a OR rand() * 0) FROM t1;
 1
 NULL
 drop table t1,t2,t3;
+set optimizer_switch=@subselect_tmp;
 #
 # LP BUG#905353 Wrong non-empty result with a constant table,
 # aggregate function in subquery, MyISAM or Aria

mysql-test/r/subselect_no_opts.result

@@ -5989,6 +5989,7 @@ SELECT ( SELECT b FROM t2 WHERE b = a OR rand() * 0) FROM t1;
 1
 NULL
 drop table t1,t2,t3;
+set optimizer_switch=@subselect_tmp;
 #
 # LP BUG#905353 Wrong non-empty result with a constant table,
 # aggregate function in subquery, MyISAM or Aria

mysql-test/r/subselect_no_scache.result

@@ -6000,6 +6000,7 @@ SELECT ( SELECT b FROM t2 WHERE b = a OR rand() * 0) FROM t1;
 1
 NULL
 drop table t1,t2,t3;
+set optimizer_switch=@subselect_tmp;
 #
 # LP BUG#905353 Wrong non-empty result with a constant table,
 # aggregate function in subquery, MyISAM or Aria

mysql-test/r/subselect_no_semijoin.result

@@ -5989,6 +5989,7 @@ SELECT ( SELECT b FROM t2 WHERE b = a OR rand() * 0) FROM t1;
 1
 NULL
 drop table t1,t2,t3;
+set optimizer_switch=@subselect_tmp;
 #
 # LP BUG#905353 Wrong non-empty result with a constant table,
 # aggregate function in subquery, MyISAM or Aria

mysql-test/t/ctype_recoding.test

@@ -210,3 +210,21 @@ drop table t1;
 create table t1(a char character set latin1 default _cp1251 0xFF);
 
 --echo End of 4.1 tests
+
+SET CHARACTER SET DEFAULT;
+--echo #
+--echo # LP BUG#944504 Item_func_conv_charset tries to execute subquery constant
+--echo # 
+SET optimizer_switch = 'in_to_exists=on';
+SET character_set_connection = utf8;
+CREATE TABLE t1 ( a VARCHAR(1) );
+INSERT INTO t1 VALUES ('m'),('n');
+CREATE VIEW v1 AS SELECT 'w' ;
+--error ER_CANT_AGGREGATE_2COLLATIONS
+SELECT * FROM t1 WHERE a < ALL ( SELECT * FROM v1 );
+drop view v1;
+drop table t1;
+SET character_set_connection = default;
+SET optimizer_switch= default;
+
+--echo #End of 5.3 tests

mysql-test/t/subselect.test

@@ -5075,8 +5075,8 @@ SELECT ( SELECT b FROM t2 WHERE b = a OR b * 0) FROM t1;
 # example with "random"
 SELECT ( SELECT b FROM t2 WHERE b = a OR rand() * 0) FROM t1;
 
-
 drop table t1,t2,t3;
+set optimizer_switch=@subselect_tmp;
 
 --echo #
 --echo # LP BUG#905353 Wrong non-empty result with a constant table,
@@ -5090,5 +5090,6 @@ SELECT a FROM t1 WHERE ( SELECT MIN(a) = 100 );
 
 drop table t1;
 
+
 --echo # return optimizer switch changed in the beginning of this test
 set optimizer_switch=@subselect_tmp;

sql/item_strfunc.h

@@ -747,7 +747,7 @@ class Item_func_conv_charset :public Item_str_func
   {
     DBUG_ASSERT(args[0]->fixed);
     conv_charset= cs;
-    if (cache_if_const && args[0]->const_item())
+    if (cache_if_const && args[0]->const_item() && !args[0]->with_subselect)
     {
       uint errors= 0;
       String tmp, *str= args[0]->val_str(&tmp);