General SQL Server Performance Tips

• Try to restrict the queries result set by returning only the particular columns from the table, not all table's columns.
This can results in good performance benefits, because SQL Server will return to client only particular columns, not all table's columns. This can reduce network traffic and boost the overall performance of the query.
• Try to avoid using SQL Server cursors, whenever possible.
SQL Server cursors can result in some performance degradation in comparison with select statements. Try to use correlated subquery or derived tables, if you need to perform row-by-row operations.
• If you need to return the total table's row count, you can use alternative way instead of SELECT COUNT (*) statement.
Because SELECT COUNT (*) statement make a full table scan to return the total table's row count, it can take very many time for the large table. There is another way to determine the total row count in a table. You can use sysindexes system table, in this case. There is ROWS column in the sysindexes table. This column contains the total row count for each table in your database. So, you can use the following select statement instead of SELECT COUNT (*): SELECT rows FROM sysindexes WHERE id = OBJECT_ID ('table_name') AND indid < 2 So, you can improve the speed of such queries in several times.
• Use table variables instead of temporary tables.
Table variables require less locking and logging resources than temporary tables, so table variables should be used whenever possible. The table variables are available in SQL Server 2000 only.
• Try to avoid using the DISTINCT clause, whenever possible.
Because using the DISTINCT clause will result in some performance degradation, you should use this clause only when it is necessary.
• Include SET NOCOUNT ON statement into your stored procedures to stop the message indicating the number of rows affected by a T-SQL statement.
This can reduce network traffic, because your client will not receive the message indicating the number of rows affected by a T-SQL statement.
• Use the select statements with TOP keyword or the SET ROWCOUNT statement, if you need to return only the first n rows.
This can improve performance of your queries, because the smaller result set will be returned. This can also reduce the traffic between the server and the clients.
• Try to use UNION ALL statement instead of UNION, whenever possible.
The UNION ALL statement is much faster than UNION, because UNION ALL statement does not look for duplicate rows, and UNION statement does look for duplicate rows, whether or not they exist.
• Try to use constraints instead of triggers, whenever possible.
Constraints are much more efficient than triggers and can boost performance. So, you should use constraints instead of triggers, whenever possible.
• Use user-defined functions to encapsulate code for reuse.
The user-defined functions (UDFs) contain one or more Transact-SQL statements that can be used to encapsulate code for reuse. Using UDFs can reduce network traffic.
• You can specify whether the index keys are stored in ascending or descending order.
For example, using the CREATE INDEX statement with the DESC option (descending order) can increase the speed of queries, which return rows in the descending order. By default, the ascending order is used.
• If you need to delete all tables’ rows, consider using TRUNCATE TABLE instead of DELETE command.
Using the TRUNCATE TABLE is much fast way to delete all tables’ rows, because it removes all rows from a table without logging the individual row deletes.
• Don't use Enterprise Manager to access remote servers over a slow link or to maintain very large databases.
Because using Enterprise Manager is very resource expensive, use stored procedures and T-SQL statements, in this case.
• Use SQL Server cursors to allow your application to fetch a small subset of rows instead of fetching all tables’ rows.
SQL Server cursors allow application to fetch any block of rows from the result set, including the next n rows, the previous n rows, or n rows starting at a certain row number in the result set. Using SQL Server cursors can reduce network traffic because the smaller result set will be returned.