SQL Optimization Tips and Index Optimization Tips | tutorials Conway AR

T-SQL Optimization Tips

• Use views and stored procedures instead of heavy-duty queries.
  This can reduce network traffic, because your client will send to server only stored procedure or view name (perhaps with some parameters) instead of large heavy-duty queries text. This can be used to facilitate permission management also, because you can restrict user access to table columns they should not see.
• 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 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 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 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.
• 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 sub-query or derived tables, if you need to perform row-by-row operations.
• Try to avoid the HAVING clause, whenever possible.
  The HAVING clause is used to restrict the result set returned by the GROUP BY clause. When you use GROUP BY with the HAVING clause, the GROUP BY clause divides the rows into sets of grouped rows and aggregates their values, and then the HAVING clause eliminates undesired aggregated groups. In many cases, you can write your select statement so, that it will contain only WHERE and GROUP BY clauses without HAVING clause. This can improve the performance of your query.
• 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 r...