Indexing Tips

•  Declare a NOT NULL indexed column if possible.   NULL requires additional server decisions  
and can be processed more simply and faster. 


•  Avoid over indexing; don't index a column just because it can be indexed. If a column is never 
going to be referred to in comparisons, then there's no need to index it. 
•  Every index created slows down table updates.  If a row is inserted, an entry must be added to 
each of the table's indexes. 


•  An index on a column that has very few distinct values is unlikely to do much good. 


•  Choose unique and non-unique indexes appropriately.  The choice may be influenced by the data type of a column and the level of distinctness. 


•  Index a column prefix rather than the entire column. Shortening the length of the key values can 
improve performance by reducing the amount of disk I/O needed. 


•  Avoid creating multiple indexes that overlap (have the same initial columns).