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().

5 files changed, 51 insertions, 6 deletions

diff --git a/sql/item.cc b/sql/item.cc
index a1482a6d634..af3917c09c1 100644
--- a/sql/item.cc
+++ b/sql/item.cc
@@ -1746,7 +1746,8 @@ bool agg_item_collations(DTCollation &c, const char *fname,
   }
   
   /* If all arguments where numbers, reset to @@collation_connection */
-  if (c.derivation == DERIVATION_NUMERIC)
+  if (flags & MY_COLL_ALLOW_NUMERIC_CONV &&
+      c.derivation == DERIVATION_NUMERIC)
     c.set(Item::default_charset(), DERIVATION_COERCIBLE, MY_REPERTOIRE_NUMERIC);
 
   return FALSE;
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
 {
diff --git a/sql/item_func.cc b/sql/item_func.cc
index 427910c3625..82310365d27 100644
--- a/sql/item_func.cc
+++ b/sql/item_func.cc
@@ -2537,7 +2537,8 @@ void Item_func_min_max::fix_length_and_dec()
   }
   if (cmp_type == STRING_RESULT)
   {
-    agg_arg_charsets_for_comparison(collation, args, arg_count);
+    agg_arg_charsets_for_string_result_with_comparison(collation,
+                                                       args, arg_count);
     if (datetime_found)
     {
       thd= current_thd;
diff --git a/sql/item_func.h b/sql/item_func.h
index e60effc352c..9198b092539 100644
--- a/sql/item_func.h
+++ b/sql/item_func.h
@@ -165,6 +165,11 @@ public:
   {
     return agg_item_charsets(c, func_name(), items, nitems, flags, item_sep);
   }
+  /*
+    Aggregate arguments for string result, e.g: CONCAT(a,b)
+    - convert to @@character_set_connection if all arguments are numbers
+    - allow DERIVATION_NONE
+  */
   bool agg_arg_charsets_for_string_result(DTCollation &c,
                                           Item **items, uint nitems,
                                           int item_sep= 1)
@@ -172,6 +177,11 @@ public:
     return agg_item_charsets_for_string_result(c, func_name(),
                                                items, nitems, item_sep);
   }
+  /*
+    Aggregate arguments for comparison, e.g: a=b, a LIKE b, a RLIKE b
+    - don't convert to @@character_set_connection if all arguments are numbers
+    - don't allow DERIVATION_NONE
+  */
   bool agg_arg_charsets_for_comparison(DTCollation &c,
                                        Item **items, uint nitems,
                                        int item_sep= 1)
@@ -179,6 +189,21 @@ public:
     return agg_item_charsets_for_comparison(c, func_name(),
                                             items, nitems, item_sep);
   }
+  /*
+    Aggregate arguments for string result, when some comparison
+    is involved internally, e.g: REPLACE(a,b,c)
+    - convert to @@character_set_connection if all arguments are numbers
+    - disallow DERIVATION_NONE
+  */
+  bool agg_arg_charsets_for_string_result_with_comparison(DTCollation &c,
+                                                          Item **items,
+                                                          uint nitems,
+                                                          int item_sep= 1)
+  {
+    return agg_item_charsets_for_string_result_with_comparison(c, func_name(),
+                                                               items, nitems,
+                                                               item_sep);
+  }
   bool walk(Item_processor processor, bool walk_subquery, uchar *arg);
   Item *transform(Item_transformer transformer, uchar *arg);
   Item* compile(Item_analyzer analyzer, uchar **arg_p,
diff --git a/sql/item_strfunc.cc b/sql/item_strfunc.cc
index ad18d5dabbe..e5c47c110f4 100644
--- a/sql/item_strfunc.cc
+++ b/sql/item_strfunc.cc
@@ -1168,7 +1168,7 @@ void Item_func_replace::fix_length_and_dec()
     char_length+= max_substrs * (uint) diff;
   }
 
-  if (agg_arg_charsets_for_comparison(collation, args, 3))
+  if (agg_arg_charsets_for_string_result_with_comparison(collation, args, 3))
     return;
   fix_char_length_ulonglong(char_length);
 }
@@ -1458,7 +1458,7 @@ void Item_func_substr::fix_length_and_dec()
 
 void Item_func_substr_index::fix_length_and_dec()
 { 
-  if (agg_arg_charsets_for_comparison(collation, args, 2))
+  if (agg_arg_charsets_for_string_result_with_comparison(collation, args, 2))
     return;
   fix_char_length(args[0]->max_char_length());
 }
@@ -1797,7 +1797,8 @@ void Item_func_trim::fix_length_and_dec()
   {
     // Handle character set for args[1] and args[0].
     // Note that we pass args[1] as the first item, and args[0] as the second.
-    if (agg_arg_charsets_for_comparison(collation, &args[1], 2, -1))
+    if (agg_arg_charsets_for_string_result_with_comparison(collation,
+                                                           &args[1], 2, -1))
       return;
   }
   fix_char_length(args[0]->max_char_length());