Special case of case-insensitive search

In Oracle10g, you might use the new case-insensitive search with a NLS_SORT=BINARY_CI command.

Pro

  • Designed for this purpose, so it's very straightforward to use

Con

  • Limited to case-insensitive searching by design

Native functional indexes

Some databases provides native functional indexes.

On these databases optimization is done simply by creating an index on UPPER(MY_COLUMN) and letting the query optimizer transparently[1] use the newly created index.

It usually work by applies a function to the data just before handing it to the index, so the function output doesn't exist in the database.

Pro

  • Very easy to use : it just feels right (you can naïvely create an index on the WHERE clause)
  • Doesn't take any extra space in the database (only the index).
  • Generic, can be used for something else than just case-insensitive searches.

Con

  • Since the data isn't stored in the database, a call to the function has to be made when
  • Functions have to be from the immutable category in the function volatility categories

Generated columns

DB2 provides something called generated columns. It's almost the same than the native indexes, except that the functional column is explicit.

Pro

  • Quite easy to use, since the column is updated and used transparently.
  • Generic, can be used for something else than just case-insensitive searches. Just make sure the optimizer uses the extra column. You might have to rewrite the request a little.

Con

  • Requires extra space in the table.
  • Removing a column can be cumbersome (in DB2 you have to recreate the whole table for example), whereas removing a simple index is much easier.
  • The extra column is returned when doing a SELECT * FROM ...[2].

Trigger-based Generated columns Emulation

If nothing else is provided, you always have the option to emulate. The solution will be trigger-based since it's one of the few perfect match for them.

So, the base idea is derived from the Generated columns : have a special extra column that represents the output of the function. An index will be created on this column and used via a manual update of the involved requests (Adding an extra WHERE clause should be more than enough, this way you might even benefit from a partial match).

Pro

  • Universal. Useful if portability is paramount.
  • Very simple : there is no need to understand advanced database features.

Con

  • Only a poor man's solution : everything is manual
  • The same than Generated columns since it's the same idea, just manually implemented.

Notes

[1] You might have to update some kind of statistics for the new index

[2] But you don't do that anyway, do you ?