Long Index is only allowed for unique keys not normal index.

mysql-test/main/long_unique.result

@@ -1405,4 +1405,61 @@ insert into t1 values( 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16,
 insert into t1 values( 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63);;
 ERROR 23000: Duplicate entry '0' for key 'a63'
 drop table t1;
+create table t1(a blob , key(a));
+Warnings:
+Note	1071	Specified key was too long; max key length is 1000 bytes
+show create table t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `a` blob DEFAULT NULL,
+  KEY `a` (`a`(1000))
+) ENGINE=MyISAM DEFAULT CHARSET=latin1
+drop table t1;
+create table t1(a blob);
+alter table t1 add index(a);
+Warnings:
+Note	1071	Specified key was too long; max key length is 1000 bytes
+show create table t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `a` blob DEFAULT NULL,
+  KEY `a` (`a`(1000))
+) ENGINE=MyISAM DEFAULT CHARSET=latin1
+drop table t1;
+create table t1(a text, key(a));
+Warnings:
+Note	1071	Specified key was too long; max key length is 1000 bytes
+show create table t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `a` text DEFAULT NULL,
+  KEY `a` (`a`(1000))
+) ENGINE=MyISAM DEFAULT CHARSET=latin1
+drop table t1;
+create table t1(a varchar(4000));
+alter table t1 add index(a);
+Warnings:
+Warning	1071	Specified key was too long; max key length is 1000 bytes
+show create table t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `a` varchar(4000) DEFAULT NULL,
+  KEY `a` (`a`(1000))
+) ENGINE=MyISAM DEFAULT CHARSET=latin1
+drop table t1;
+create table t1 (pk int, a int, b int, primary key(pk), key(pk,a));
+alter table t1 modify a text;
+ERROR 42000: Specified key was too long; max key length is 1000 bytes
+alter table t1 modify a varchar(1000);
+ERROR 42000: Specified key was too long; max key length is 1000 bytes
+show create table t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `pk` int(11) NOT NULL,
+  `a` int(11) DEFAULT NULL,
+  `b` int(11) DEFAULT NULL,
+  PRIMARY KEY (`pk`),
+  KEY `pk` (`pk`,`a`)
+) ENGINE=MyISAM DEFAULT CHARSET=latin1
+drop table t1;
 set @@GLOBAL.max_allowed_packet= @allowed_packet;

mysql-test/main/long_unique.test

@@ -512,4 +512,34 @@ while ($count)
 --eval $insert_data_2
 drop table t1;
 
+#
+# non-unique long indexes are automatically shortened
+#
+create table t1(a blob , key(a));
+show create table t1;
+drop table t1;
+create table t1(a blob);
+alter table t1 add index(a);
+show create table t1;
+drop table t1;
+
+create table t1(a text, key(a));
+show create table t1;
+drop table t1;
+create table t1(a varchar(4000));
+alter table t1 add index(a);
+show create table t1;
+drop table t1;
+
+#
+# somewhat inconsistently, the following is an error
+#
+create table t1 (pk int, a int, b int, primary key(pk), key(pk,a));
+--error ER_TOO_LONG_KEY
+alter table t1 modify a text;
+--error ER_TOO_LONG_KEY
+alter table t1 modify a varchar(1000);
+show create table t1;
+drop table t1;
+
 set @@GLOBAL.max_allowed_packet= @allowed_packet;

sql/sql_table.cc

@@ -3941,13 +3941,15 @@ mysql_prepare_create_table(THD *thd, HA_CREATE_INFO *create_info,
             column->length= MAX_LEN_GEOM_POINT_FIELD;
           if (!column->length)
           {
-            if (key->type == Key::PRIMARY)
+            if (key->type == Key::UNIQUE)
+              is_hash_field_needed= true;
+            else if (key->type == Key::MULTIPLE)
+              column->length= file->max_key_length() + 1;
+            else
             {
               my_error(ER_BLOB_KEY_WITHOUT_LENGTH, MYF(0), column->field_name.str);
               DBUG_RETURN(TRUE);
             }
-            else
-              is_hash_field_needed= true;
           }
         }
 #ifdef HAVE_SPATIAL