Simply understanding a nine-step tuning process is not enough to be able to make a system work efficiently. You need a formal, quantitative way to measure performance. You also need some specific vocabulary to avoid any possible misunderstanding. The vocabulary list may vary somewhat, but the following terms are fundamental: Command. An atomic part of […]
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One of Oracle’s more interesting but little used or understood facilities is its CONNECT BY clause. Put simply, this method is used to report, in order, the branches of a family tree. Such trees are encountered often—the genealogy of human families, livestock, horses; corporate management, company divisions, manufacturing; literature, ideas, evolution, scientific research, theory; and […]
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People who have worked with computers for any period of time are familiar with the concept of a file; it’s a place on disk where information is stored, and it has a name. Its size is usually not fixed: If you add information to the file, it grows larger and takes up more disk space, […]
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Most single-value functions in Oracle are pretty straightforward. This article gives short examples of the major functions, and it shows both the results of the functions and how they correspond to columns, rows, and lists. After the examples, you’ll learn how to combine these functions. A table named MATH was created to show the calculation effects […]
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MySQL® is one of the most popular relational database management systems being used today. Its popularity with SQL admins who manage data sets puts it at the back end of many tiered applications. But with great popularity comes great responsibility, especially for an IT admin who is new to monitoring and managing MySQL instances. This is a different […]
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One of the best things about being a DBA is that I am always learning. As a long time DBA (+25 years), who has worked with about every database type imaginable, I find that my latest challenge is to keep up with all the new features and functionality the latest versions have to offer. This […]
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Here are the rules Oracle uses to execute each query, and the order in which execution takes place: Choose rows based on the WHERE clause. Group those rows together based on the GROUP BY clause. Calculate the results of the group functions for each group. Choose and eliminate groups based on the HAVING clause. Order […]
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The issue of whether allowing SQL to do automatic conversion of datatypes is a good practice or not has arguments on either side. On one hand, this practice considerably simplifies and reduces the functions necessary to make a SELECT statement work. On the other hand, if your assumption about what will be in the column […]
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If your applications use only two-digit values for years, you may encounter problems related to years around 2000. If you only specify two digits of a year (such as “98” for “1998”), you are relying on the database to specify the century value (the “19”) when the record is inserted. If you are putting in […]
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Group-value functions in Oracle treat NULL values differently than single-value functions do. Group functions (other than COUNT(*)) ignore NULL values and calculate a result without considering them. Take AVG as an example. Suppose you have a list of 100 friends and their ages. If you picked 20 of them at random and averaged their ages, […]
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It is worthwhile to sum up in a single place all the major issues in designing Oracle database applications—thus “The Commandments” (or perhaps “The Suggestions”). Their presentation does not assume that you need to be told what to do, but rather that you are capable of making rational judgments and can benefit from the experience […]
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One of the often-neglected steps in building software is understanding the end user’s job—the tasks that computer automation is intended to support. Occasionally, this is because the application itself is quite specialized; more often, it is because the approach to design tends to be data oriented. Frequently, these are the major questions asked in the […]
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