Fragmenting the index using same distribution scheme as the table

You fragment an index with the same distribution scheme as the table when you create the index that uses the same fragment expressions as the table.

A common fragmentation strategy is to fragment indexes in the same way as the tables but to specify different dbspaces for the index fragments. This fragmentation strategy of putting the index fragments into different dbspaces from the table can improve the performance of operations such as backup and recovery.

For example, suppose you create a fragmented table and index with the following SQL statements:
CREATE TABLE tb1(a int, b int) 
   FRAGMENT BY EXPRESSION
      (a >=0 AND a < 5) IN db1,
      (a >=5 AND a <10) IN db2,
      (a >=10 AND a <15) IN db3;

CREATE INDEX idx1 on tb1(a)
   FRAGMENT BY EXPRESSION
      (a >=0 AND a< 5) IN db4,
      (a >=5 AND a< 10) IN db5,
      (a >=10 AND a<15) IN db6;                
Suppose that you then decide to detach the data in the third fragment with the following SQL statement:
ALTER FRAGMENT ON TABLE tb1 
   DETACH db3 tb3;

Because the distribution scheme of the index is the same as the table, the ALTER FRAGMENT DETACH statement does not rebuild the index after the detach operation. The database server drops the fragment of the index in dbspace db3, updates the system catalog tables, and eliminates the index build.