NDB Cluster Disk Data Tables uses disk storage can be indexed; when this is done, the column’s storage type is changed to  MEMORY automatically. By “implicitly” , we mean a column whose storage type is not declared, but which is which inherited from the parent table. In the following CREATE TABLE statement (using the tablespace  ts_1 defined previously), columns  c2  and  c3  use disk storage implicitly: Because  c2 ,  c3 , and  c4  are themselves not declared with  STORAGE DISK , it is possible to index them. Here, we add indexes to  c2  and  c3 , using, respectively,  CREATE INDEX  and  ALTER TABLE : SHOW CREATE TABLE  confirms that the indexes were added. You can see using  ndb_desc  that the indexed columns (emphasized text) now use in-memory rather than on-disk storage: 4502 shell>  ./ndb_desc -d test t1 -- t1 -- Version: 33554433 Fragment type: HashMapPartition K Value: 6 Min load factor: 78 Max load factor: 80 Temporary table: no Number of attributes: 4 Number of primary keys: 1 Length of frm data: 317 Max Rows: 0 Row Checksum: 1 Row GCI: 1 SingleUserMode: 0 ForceVarPart: 1 PartitionCount: 4 FragmentCount: 4 PartitionBalance: FOR_RP_BY_LDM ExtraRowGciBits: 0 mysql>  SHOW CREATE TABLE ti\G *************************** 1. row *************************** Table: ti Create Table: CREATE TABLE ‘ti‘ ( ‘c1‘ int(11) NOT NULL, ‘c2‘ int(11) DEFAULT NULL, ‘c3‘ int(11) DEFAULT NULL, ‘c4‘ int(11) DEFAULT NULL, PRIMARY KEY (‘c1‘), KEY ‘i1‘ (‘c2‘), KEY ‘i2‘ (‘c3‘) ) /*!50100 TABLESPACE ‘ts_1‘ STORAGE DISK */ ENGINE=ndbcluster DEFAULT CHARSET=latin1 1 row in set (0.00 sec) mysql>  CREATE INDEX i1 ON ti(c2); Query OK, 0 rows affected (2.72 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql>  ALTER TABLE ti ADD INDEX i2(c3); Query OK, 0 rows affected (0.92 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql>  CREATE TABLE ti ( -> c1 INT PRIMARY KEY, -> c2 INT, -> c3 INT, -> c4 INT ->  ) -> STORAGE DISK -> TABLESPACE ts_1 -> ENGINE NDBCLUSTER; Query OK, 0 rows affected (1.31 sec)