SQL Server Performance Tuning
How do I find the most frequently occurring value for all data in a table? How do I find that value per group?
As always, there is more than one way to get a correct result. But which way gives you the best performance? Let’s first build a simplified test scenario to illustrate what we’re after. CREATE TABLE #t (ArticleGroup CHAR(2), Price DECIMAL(8,2)) INSERT INTO #t VALUES(‘SP’, 1.2) INSERT INTO #t VALUES(‘SP’, 1.2) INSERT INTO #t VALUES(‘SP’, 2.1) […]
How can I determine the maximum value for each data? And which option provides the best performance?
One of the most common requirements is to generate a list of, say, customers along with their last order date. Or, generally speaking, a list of distinct values in one table along with a corresponding maximum value from another table. To solve such problems you basically have three different alternatives. Let’s have a look at […]
Question The following two queries produce the same results. Is one or the other versions of these two queries more efficient than the other? SELECT DISTINCT productcode FROM sales SELECT productcode FROM sales GROUP BY productcode Answer The goal of both of the above queries is to produce a list of distinct product codes from […]
I want to add an identity or unique identifier column to a table in order to ensure that each row is unique. For best performance, which one should I use?
One of the key aspects of database table design is to ensure what is called entity integrity. What this means is that you need to ensure that each row in your database tables is unique. If you don’t take the proper precautions, it is possible that one or more rows of your table might be […]
Question Which of the following joins will produce better performance? ANSI JOIN Syntax SELECT fname, lname, departmentFROM names INNER JOIN departments ON names.employeeid = departments.employeeid Former Microsoft JOIN Syntax SELECT fname, lname, departmentFROM names, departmentsWHERE names.employeeid = departments.employeeid AnswerSQL Server supports two variations of performing JOINs: the ANSI JOIN syntax and the former Microsoft JOIN […]
I don’t like to delete records in our production database, even though we will never need them again. Does this affect performance?
Question I don’t like to delete records in our production database, even though we will never need them again. Because of this, I have included an extra column in every table called the “ACTIVE_FLAG” that is set to one character in length that contains either an “a” for active records or a “d” for deleted […]
In my stored procedures I have the option of calling the same data from either a table or a view. For best performance, should I be calling a table or a view?
Anytime you call data from a view instead of a table, there is additional overhead, which can hurt performance. Because of this, optimum performance can be had by calling your data directly from a table, not a view. If you don’t use the stored procedure often, the performance difference will not be noticeable if you […]
Yes, SQL Server’s performance can be affected by using NULLS in your database. There are several reasons for this. First, NULLS that appear in fixed length columns (CHAR) take up the entire size of the column. So if you have a column that is 25 characters wide, and a NULL is stored in it, then […]
Question I understand that I should avoid the use of SQL Server cursors in order to increase an application’s performance. Can you provide some ways that I might be able to avoid using cursors in my applications? AnswerA SQL Server cursor should only be considered in situations where you need to scroll through a set […]
This is virtually no difference in performance between using SET or SELECT to assign values. In most cases you will want to use the ANSI standard, which says you should use SELECT. See the SQL Server Books Online for the exact syntax for both options.