sql_table.cc:

  Bug#11657 Creation of secondary index fails:

  If TINYBLOB key part length is 255, it is equal
  to field length. For BLOB, unlike for CHAR/VARCHAR,
  we should keep a non-zero key part length, otherwise
  "BLOB/TEXT column used in key specification without a key length"
  error is produced afterwards.

type_blob.result, type_blob.test:
  fixing tests accordinly


sql/sql_table.cc:
  Bug#11657 Creation of secondary index fails
  For TINYBLOB key part length can be equal to field length.
  We should still keep a non-zero key part length,
mysql-test/t/type_blob.test:
  fixing tests accordinly
mysql-test/r/type_blob.result:
  fixing tests accordinly

mysql-test/r/type_blob.result

@@ -703,3 +703,18 @@ select max(i) from t1 where c = '';
 max(i)
 4
 drop table t1;
+create table t1 (a int, b int, c tinyblob, d int, e int);
+alter table t1 add primary key (a,b,c(255),d);
+alter table t1 add key (a,b,d,e);
+show create table t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `a` int(11) NOT NULL default '0',
+  `b` int(11) NOT NULL default '0',
+  `c` tinyblob NOT NULL,
+  `d` int(11) NOT NULL default '0',
+  `e` int(11) default NULL,
+  PRIMARY KEY  (`a`,`b`,`c`(255),`d`),
+  KEY `a` (`a`,`b`,`d`,`e`)
+) ENGINE=MyISAM DEFAULT CHARSET=latin1
+drop table t1;

mysql-test/t/type_blob.test

@@ -394,4 +394,11 @@ INSERT t1 (i, c) VALUES (1,''),(2,''),(3,'asdfh'),(4,'');
 select max(i) from t1 where c = '';
 drop table t1;
 
-
+#
+# Bug#11657: Creation of secondary index fails
+#
+create table t1 (a int, b int, c tinyblob, d int, e int);
+alter table t1 add primary key (a,b,c(255),d);
+alter table t1 add key (a,b,d,e);
+show create table t1;
+drop table t1;

sql/sql_table.cc

@@ -3400,7 +3400,8 @@ bool mysql_alter_table(THD *thd,char *new_db, char *new_name,
          */
         if (!Field::type_can_have_key_part(cfield->field->type()) ||
             !Field::type_can_have_key_part(cfield->sql_type) ||
-            cfield->field->field_length == key_part_length ||
+            (cfield->field->field_length == key_part_length &&
+             !f_is_blob(key_part->key_type)) ||
 	    (cfield->length && (cfield->length < key_part_length /
                                 key_part->field->charset()->mbmaxlen)))
 	  key_part_length= 0;			// Use whole field