sqlperformance

Recently I found a couple of tables in a Database with no Clustered Indexes defined. But there are non-clustered indexes defined, so they are on HEAP. On analysis I found that select statements were using filter on the columns defined in non-clustered indexes. Not having a clustered index on these tables affect performance? It's hard to state this more succinctly than SQL Server MVP Brad McGehee : As a rule of thumb, every table should have a clustered index. Generally, but not always, the clustered index should be on a column that monotonically increases–such as an identity column, or some

When should I use KEY , PRIMARY KEY , UNIQUE KEY and INDEX ? KEY and INDEX are synonyms in MySQL. They mean the same thing. In databases you would use indexes to improve the speed of data retrieval. An index is typically created on columns used in JOIN , WHERE , and ORDER BY clauses. Imagine you have a table called users and you want to search for all the users which have the last name 'Smith'. Without an index, the database would have to go through all the records of the table: this is slow, because the more records you have in your database, the more work it has to do to find the result. On