When you create an additional column index, the CREATE INDEX command creates the new index as part of the individual table and as part of any join indexes that include the column. CMP and multicolumn HG indexes are the only exception to this rule.
If the existing column indexes in the individual table already contain data, the CREATE INDEX statement also inserts data into the new index from an existing index. This ensures data integrity among all the column indexes for columns within an individual table. Data is also inserted and synchronized automatically when you add an index to previously loaded tables that are part of a join index. For information on synchronization, see “Synchronizing join indexes”.
This capability is useful if you discover that a column needs an additional index after you have already inserted data. This allows you to add the index without having to start over.
Inserting data from an existing index can be slow. It
is always faster to create all the appropriate indexes before you
insert data, then insert into all of them at once, with either the LOAD
TABLE or INSERT statement.
