Bug#31384 DATE_ADD() and DATE_SUB() return binary data

Problem: DATE_ADD() is a hybrid function and can return
DATE, DATETIME or VARCHAR data type depending on arguments.

In case of VARCHAR data type, DATE_ADD() reported "binary" character set,
which was wrong.

Fix: make DATE_ADD() return @character_set_connection in VARCHAR context.
 @ mysql-test/include/ctype_numconv.inc
   Adding tests
 @ mysql-test/r/ctype_binary.result
   Adding tests
 @ mysql-test/r/ctype_cp1251.result
   Adding tests
 @ mysql-test/r/ctype_latin1.result
   Adding tests
 @ mysql-test/r/ctype_ucs.result
   Adding tests
 @ mysql-test/r/ctype_utf8.result
   Adding tests
 @ sql/item_strfunc.cc
  - Moving code from Item_str_ascii_func::val_str() to
  Item_str_func::val_str_from_val_str_ascii(), as
  this code needs to be shared by Item_date_add_interval.
  - Adding str2 parameter to be used as a buffer, instead of
   using private ascii_buf member.
 @ sql/item_strfunc.h
  - Moving code from Item_str_ascii_func::val_str() to
  Item_str_func::val_str_from_val_str_ascii()
  - Removing "String *val_str_convert_from_ascii(String *str, String *ascii_buf)"
    prototype as it was neither used nor declared.
 @ sql/item_timefunc.h
  - Overwriting parent's charset_for_protocol() method,
    becase we need to behave differenlty in VARCHAR and DATE/DATETYPE context.
  - Adding ascii_buf for conversion.
  - Adding val_str_ascii() prototype.
  - Adding val_str() which uses newly added
    Item_str_func::val_str_from_val_str_ascii(),
    passing ascii_buf as a conversion buffer.

1 files changed, 16 insertions, 3 deletions

diff --git a/sql/item_timefunc.cc b/sql/item_timefunc.cc
index 73b8b6047e0..3d587ace335 100644
--- a/sql/item_timefunc.cc
+++ b/sql/item_timefunc.cc
@@ -2205,8 +2205,6 @@ void Item_date_add_interval::fix_length_and_dec()
   enum_field_types arg0_field_type;
 
   maybe_null=1;
-  fix_length_and_charset_datetime(MAX_DATETIME_FULL_WIDTH);
-  value.alloc(max_length);
 
   /*
     The field type for the result of an Item_date function is defined as
@@ -2231,6 +2229,21 @@ void Item_date_add_interval::fix_length_and_dec()
     else
       cached_field_type= MYSQL_TYPE_DATETIME;
   }
+
+  if (cached_field_type == MYSQL_TYPE_STRING)
+  {
+    /* Behave as a usual string function when return type is VARCHAR. */
+    fix_length_and_charset(MAX_DATETIME_FULL_WIDTH, default_charset());
+  }
+  else
+  {
+    /*
+      Follow the "Number-to-string conversion" rules as in WorkLog 2649
+      when return type is DATE or DATETIME.
+    */
+    fix_length_and_charset_datetime(MAX_DATETIME_FULL_WIDTH);
+  }
+  value.alloc(max_length);
 }
 
 
@@ -2253,7 +2266,7 @@ bool Item_date_add_interval::get_date(MYSQL_TIME *ltime, uint fuzzy_date)
 }
 
 
-String *Item_date_add_interval::val_str(String *str)
+String *Item_date_add_interval::val_str_ascii(String *str)
 {
   DBUG_ASSERT(fixed == 1);
   MYSQL_TIME ltime;