Dick Kniep <dick@xxxxxxxx> writes: > Does this mean that if you have a table that has many rows, and 95% of the > rows contain a NULL value for a field, that indexing will be useless, because > it will always do a tablescan? Any time you have 95% of the rows of the table with the same value you're probably going to have to think harder than usual about indexing strategies. You might consider constructing your index with "WHERE a IS NOT NULL" since otherwise 95% of your index is going to be full of records that aren't selective enough to be useful anyways. If you access your table with "WHERE a = ?" then it will undoubtedly use the index effectively. You're accessing less than 5% (presumably much less), so the index is useful. -- greg
