IJSRP JUNE 2012 Online Print Version - IJSRP.ORG

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International Journal of Scientific and Research Publications, Volume 2, Issue 6, June <strong>2012</strong> 35 ISSN 2250-3153 [8] Harman, E.A., Rosenstein, M.T., Frykman, P.N., Rosenstein, R.M., and Kraemer, W.J.. Estimation of Human Power Output From Vertical Jump. Journal of Applied Sport Science Research, 1991; 5(3), 116-20. [9] Johnson DL and Bahamonde R.. Power Output Estimate in University Athletes. Journal of strength and Conditioning Research, 1996 ; 10(3), 161- 66. [10] Brooks, G.A., Fahey, T.D., White, T.P., and Baldwin, K.M. Exercise Physiology:Human Bioenergetics and its Applications, 3rd ed. Mountain View, CA: Mayfield Publishing Company, 2000. [11] Hoffman, J.R., S. Epstein, M. Einbinder & Y. Weinstein. A comparison between the Wingate anaerobic power test to both vertical jump and line drill tests in basketball players. J. Strength Cond. Res. 2000 : 14:261–64. [12] Bosco, C., P. Luhtanen & P.V. Komi. A simple method for measurement of mechanical power in jumping. Eur. J. Appl. Physiol. 1983 ; 50:273–82. First Author – Purvi K. Changela, Lecturer, Shri K K Sheth Physiotherapy College, Rajkot Second Author – Sarla Bhatt, Principle, Shri K K Sheth Physiotherapy College, Rajkot www.ijsrp.org
International Journal of Scientific and Research Publications, Volume 2, Issue 6, June <strong>2012</strong> 36 ISSN 2250-3153 SQL Server Query Optimization Techniques - Tips for Writing Efficient and Faster Queries Abstract- SQL statements can be used to retrieve data from the any database. To get same results we need to write different SQL queries. For better performance we need to use best, faster and efficient queries. So we need SQL query tuning based on the business and user requirements. This paper covers how these SQL queries can be optimized for better performance. Query optimization subject is very deep but we will try to cover the most important points. In this paper I am not focusing on, indepth analysis of database but simple query tuning tips & tricks which can be applied to gain immediate performance gain. T I. INTRODUCTION he best way to tune performance is to try to write your queries in a number of different ways and compare their reads and execution plans. Here are various techniques that you can use to try to optimize your database queries. Query optimization is an important skill for SQL developers and database administrators (DBAs). In order to improve the performance of SQL queries, developers and DBAs need to understand the query optimizer and the techniques it uses to select an access path and prepare a query execution plan. Query tuning involves knowledge of techniques such as cost-based and heuristic-based optimizers, plus the tools an SQL platform provides for explaining a query execution plan. II. QUERY PERFORMANCE OVERVIEW USING STATISTICS IO There are different ways to determine the best way to write queries. Two of common methods are looking at the number of logical reads produced by the query and looking at graphical execution plans provided by SQL Server Management Studio. For determining the number of logical reads, you can turn the STATISTICS IO option ON. Consider this query: SET STATISTICS IO ON SELECT * FROM tablename The following is returned in the Messages window in SQL Server Management Studio: Table ‗tablename‘. Scan count 1, logical reads 33, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. There are several bits of data returned by STATISTICS IO, but we are concerned with the logical reads portion because it will tell us the number of pages read from the data cache. This is the most helpful because it will stay constant when I run the same Navita Kumari Innovation Centre - Baba Farid Group of Institutions query, which is important because there are sometimes external factors that might vary the execution time of my queries, such as locking by other queries. When tuning SQL queries, our goal should be to get the number of logical reads as low as possible. As fewer logical reads typically lead to faster execution times. III. GENERAL TIPS FOR QUERY OPTIMIZATION Specific Column Names instead of * in SELECT Query The SQL query becomes faster if you use the actual columns names in SELECT statement instead of than '*'. So we need to restrict the queries result set by selecting only the particular columns from the table, rather than all columns from a particular table. This results in performance benefits, as SQL Server will return only particular columns to the client, not all columns of a table. This will help reduce the network traffic and also boost the overall performance of the query. Example: Write the query as SELECT col_1, col_2, col_3, col_4, subject FROM table_name; Instead of: SELECT * FROM table_name; Alternatives of COUNT (*) for returning total tables row count If we need to return the table's row count, we can use alternative ways instead of the SELECT COUNT (*) statement. As SELECT COUNT (*) statement makes a full table scan to return the table's row count, it can take much time for the large tables. There is another way to determine the total row count of a table. We can use sysindexes system table. There is a ROWS column in the sysindexes table. This ROWS column contains the total row count for each table in a particular database. So, we can use the following select statement instead of ―SELECT COUNT (*): SELECT rows FROM sysindexes WHERE id = OBJECT_ID ('table_name') AND indid < 2‖. So we can improve the speed of such queries thus resulting in better performance. Try to avoid HAVING Clause in Select statements HAVING clause is used to filter the rows after all the rows are selected and is used like a filter. Try not to use HAVING clause for any other purposes. For Example: Write the query as SELECT Col_1, count (Col_1) FROM table_name WHERE col_1!= ‗testvalue1‘ www.ijsrp.org
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