Merge from 4.1.

mysql-test/r/type_float.result:
  Auto merged
mysql-test/t/type_float.test:
  Auto merged
sql/field_conv.cc:
  Auto merged
sql/table.cc:
  Merge warning of multi-byte charset being applied
  to table of unknown charset.

mysql-test/r/type_float.result

@@ -146,6 +146,15 @@ drop table t1;
 create table t1 (f float(54));
 ERROR 42000: Incorrect column specifier for column 'f'
 drop table if exists t1;
+create table t1 (d1 double, d2 double unsigned);
+insert into t1 set d1 = -1.0;
+update t1 set d2 = d1;
+Warnings:
+Warning	1264	Data truncated; out of range for column 'd2' at row 1
+select * from t1;
+d1	d2
+-1	0
+drop table t1;
 create table t1 (f float(4,3));
 insert into t1 values (-11.0),(-11),("-11"),(11.0),(11),("11");
 Warnings:

mysql-test/t/type_float.test

@@ -94,6 +94,13 @@ create table t1 (f float(54));	# Should give an error
 drop table if exists t1;
 --enable_warnings
 
+# Don't allow 'double unsigned' to be set to a negative value (Bug #7700)
+create table t1 (d1 double, d2 double unsigned);
+insert into t1 set d1 = -1.0;
+update t1 set d2 = d1;
+select * from t1;
+drop table t1;
+
 # Ensure that maximum values as the result of number of decimals
 # being specified in table schema are enforced (Bug #7361)
 create table t1 (f float(4,3));

sql/field_conv.cc

@@ -584,6 +584,7 @@ void field_conv(Field *to,Field *from)
   if (to->real_type() == from->real_type())
   {
     if (to->pack_length() == from->pack_length() &&
+        !(to->flags & UNSIGNED_FLAG && !(from->flags & UNSIGNED_FLAG)) &&
 	to->real_type() != FIELD_TYPE_ENUM &&
 	to->real_type() != FIELD_TYPE_SET &&
         from->charset() == to->charset() &&

sql/table.cc

@@ -166,6 +166,14 @@ int openfrm(THD *thd, const char *name, const char *alias, uint db_stat,
   if (!share->table_charset)
   {
     /* unknown charset in head[38] or pre-3.23 frm */
+    if (use_mb(default_charset_info))
+    {
+      /* Warn that we may be changing the size of character columns */
+      sql_print_warning("'%s' had no or invalid character set, "
+                        "and default character set is multi-byte, "
+                        "so character column sizes may have changed",
+                        name);
+    }
     share->table_charset= default_charset_info;
   }
   share->db_record_offset= 1;