Composite Indexes
OMNIDEX lets you create composite indexes that combine multiple columns
or parts of columns. You can create both MDK and ASK composite indexes
simply by specifying them within either the MDK or ASK installation section
of either DBINSTAL or the installation batch file. All composite indexes
let you:
- combine several columns into one index
- isolate part of a field into an index
- rearrange the order of bytes in an index
In addition, you can create two special types of ASK composite indexes:
- index-only access indexes which are useful for very-high speed searches
and data warehousing installations.
- aggregate indexes which quickly calculate and report summaries of
numeric data for groups of rows.
Composite Index Rules
Certain rules apply when designing and creating composite indexes:
- Each composite index must have a unique name. If you create both a
MDK and a ASK composite key with identical elements, you must name each
uniquely.
- Composite index components must come from the current table. If you
are installing interactively with DBINSTAL, enter H at a Component prompt
for a list of eligible columns.
- A column, or part of a column, can be used in more than one composite
index. You could, for example, rearrange or combine a SHIP_DATE column
with other columns in several composite indexes.
MDK composite keys:
- are indexed as ASCII (type X) by default
- can combine only character types
- if created from binary columns, must contain only one component and
be typecast as a valid binary data type.
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