Bug#11926811 / Bug#60625 Illegal mix of collations

Problem: comparison of a DATETIME sp variable and NOW()
led to Illegal mix of collations error when 
character_set_connection=utf8.
Introduced by "WL#2649 Number-to-string conversions".

Error happened in Arg_comparator::set_compare_func(),
because the first argument was errouneously converted to utf8,
while the second argument was not.

Fix: separate agg_arg_charsets_for_comparison() into two functions:

- agg_arg_charsets_for_comparison() - for pure comparison,
  when we don't need to return any string result and therefore
  don't need to convert arguments to @@character_set_connection:
    SELECT a = b;

- agg_arg_charsets_for_string_results_with_comparison() - when
  we need to return a string result, but we also need to do
  comparison internally: SELECT REPLACE(a,b,c)
  If all arguments are numbers:
    SELECT REPLACE(123,2,3) -> 133
  we convert arguments to @@character_set_connection.


  @ mysql-test/include/ctype_numconv.inc
  @ mysql-test/r/ctype_binary.result
  @ mysql-test/r/ctype_cp1251.result
  @ mysql-test/r/ctype_latin1.result
  @ mysql-test/r/ctype_ucs.result
  @ mysql-test/r/ctype_utf8.result
  Adding tests

  @ sql/item.cc
  @ sql/item.h
  @ sql/item_func.cc
  @ sql/item_func.h
  @ sql/item_strfunc.cc

  Introducing and using new function
   agg_item_charsets_for_string_result_with_comparison() and
  its Item_func wrapper agg_arg_charsets_for_string_result_with_comparison().

1 files changed, 18 insertions, 1 deletions

diff --git a/sql/item.h b/sql/item.h
index 3e67ffacfc8..96b8c9eb2e4 100644
--- a/sql/item.h
+++ b/sql/item.h
@@ -53,6 +53,8 @@ char_to_byte_length_safe(uint32 char_length_arg, uint32 mbmaxlen_arg)
                                  (i.e. constant).
   MY_COLL_ALLOW_CONV           - allow any kind of conversion
                                  (combination of the above two)
+  MY_COLL_ALLOW_NUMERIC_CONV   - if all items were numbers, convert to
+                                 @@character_set_connection
   MY_COLL_DISALLOW_NONE        - don't allow return DERIVATION_NONE
                                  (e.g. when aggregating for comparison)
   MY_COLL_CMP_CONV             - combination of MY_COLL_ALLOW_CONV
@@ -62,6 +64,7 @@ char_to_byte_length_safe(uint32 char_length_arg, uint32 mbmaxlen_arg)
 #define MY_COLL_ALLOW_SUPERSET_CONV   1
 #define MY_COLL_ALLOW_COERCIBLE_CONV  2
 #define MY_COLL_DISALLOW_NONE         4
+#define MY_COLL_ALLOW_NUMERIC_CONV    8
 
 #define MY_COLL_ALLOW_CONV (MY_COLL_ALLOW_SUPERSET_CONV | MY_COLL_ALLOW_COERCIBLE_CONV)
 #define MY_COLL_CMP_CONV   (MY_COLL_ALLOW_CONV | MY_COLL_DISALLOW_NONE)
@@ -1561,7 +1564,8 @@ agg_item_charsets_for_string_result(DTCollation &c, const char *name,
                                     int item_sep= 1)
 {
   uint flags= MY_COLL_ALLOW_SUPERSET_CONV |
-              MY_COLL_ALLOW_COERCIBLE_CONV;
+              MY_COLL_ALLOW_COERCIBLE_CONV |
+              MY_COLL_ALLOW_NUMERIC_CONV;
   return agg_item_charsets(c, name, items, nitems, flags, item_sep);
 }
 inline bool
@@ -1574,6 +1578,19 @@ agg_item_charsets_for_comparison(DTCollation &c, const char *name,
               MY_COLL_DISALLOW_NONE;
   return agg_item_charsets(c, name, items, nitems, flags, item_sep);
 }
+inline bool
+agg_item_charsets_for_string_result_with_comparison(DTCollation &c,
+                                                    const char *name,
+                                                    Item **items, uint nitems,
+                                                    int item_sep= 1)
+{
+  uint flags= MY_COLL_ALLOW_SUPERSET_CONV |
+              MY_COLL_ALLOW_COERCIBLE_CONV |
+              MY_COLL_ALLOW_NUMERIC_CONV |
+              MY_COLL_DISALLOW_NONE;
+  return agg_item_charsets(c, name, items, nitems, flags, item_sep);
+}
+
 
 class Item_num: public Item_basic_constant
 {