INDEX tips

When to Create an Index
You should create an index if:
• A column contains a wide range of values
• A column contains a large number of null values
• One or more columns are frequently used together in a WHERE clause or a join condition
• The table is large and most queries are expected to retrieve less than 2 to 4 percent of the rows


When Not to Create an Index
It is usually not worth creating an index if:
• The table is small
• The columns are not often used as a condition in the query
• Most queries are expected to retrieve more than 2 to 4 percent of the rows in the table
• The table is updated frequently
• The indexed columns are referenced as part of an expression