When should you not add an index?

When should we not use indexes?

Indexes should not be used on columns that return a high percentage of data rows when used as a filter condition in a query's WHERE clause. For instance, you would not have an entry for the word "the" or "and" in the index of a book. Tables that have frequent, large batch update jobs run can be indexed.

What is a disadvantage to using an index?

There is some overhead to an index. The index itself occupies space on disk and memory (when used). So, if space or memory are issues then too many indexes could be a problem. When data is inserted/updated/deleted, then the index needs to be maintained as well as the original data.

When should you add an index to a table?

Index the Correct Tables and Columns Create an index if you frequently want to retrieve less than about 15% of the rows in a large table. This threshold percentage varies greatly, however, according to the relative speed of a table scan and how clustered the row data is about the index key.

Why it is not recommended to create indexes on small tables?

Indexing small tables may not be optimal because it can take the query optimizer longer to traverse the index searching for data than to perform a simple table scan. Therefore, indexes on small tables might never be used, but must still be maintained as data in the table changes.