Restrictions on Fragmentation Expressions

The following restrictions apply to the expression:

• Each fragment expression can contain columns only from the current table, with data values only from a single row.
• The columns contained in a fragment expression must be the same as the indexed columns or a subset of the indexed columns.
• The expression must return a BOOLEAN (true or false) value.
• No subqueries, aggregates, user-defined routines, nor references to fields of a ROW type column are valid.
• The built-in CURRENT, DATE, and TODAY functions are not valid.

In Extended Parallel Server, you can fragment indexes on any column of a table, even if the table spans multiple coservers. The columns that you specify in the FRAGMENT BY clause do not need to be part of the index key.

Detached indexes of Extended Parallel Server can be either locally detached or globally detached. A locally detached index is an index in which, for each data tuple in a table, the corresponding index tuple is guaranteed to be on the same coserver. The table and index fragmentation strategies need not be identical if co-locality can be guaranteed. If the data tuple and index tuple co-locality do not exist, then the index is a globally-detached index. For performance implications of globally-detached indexes, see your IBM Informix Performance Guide. For more information on options for distribution strategies in Extended Parallel Server, see Fragmenting by EXPRESSION, Fragmenting by HASH (XPS), and Fragmenting by HYBRID (XPS), respectively, in the description of the CREATE TABLE statement.