TAILIEUCHUNG - SQL PROGRAMMING STYLE- P27

SQL PROGRAMMING STYLE- P27:Im mot trying to teach you to program in SQL in this book. You might want to read that again. If that is what you wanted, there are better books. This ought to be the second book you buy, not the first. I assume that you already write SQL at some level and want to get better at it. If you want to learn SQL programming tricks, get a copy of my other book, SQL for Smarties (3rd edition, 2005). | Encoding Scheme Types 87 A good heuristic is to order the values in some natural manner if one exists in the data so that table lookup will be easier. Chronological order 1 occurs before 2 or procedural order 1 must be done before 2 is often a good choice. Another good heuristic is to order the values from most common to least common. That way you will have shorter codes for the most common cases. Other orderings could be based on physical characteristics such as largest to smallest rainbow-color order and so on. After arguing for a natural order in the list I must admit that the most common scheme is alphabetical order because it is simple to implement on a computer and makes it easy for a person to look up values in a table. ANSI standard Structure for the Identification of Counties of the United States for Information Interchange encodes county names within a state by first alphabetizing the names and then numbering them from one to whatever is needed. Measurement Encoding A measurement encoding is given in some unit of measure such as pounds meters volts or liters. This can be done in one of two ways. The column contains an implied unit of measure and the numbers represent the quantity in that unit but sometimes the column explicitly contains the unit. The most common example of the second case would be money fields where a dollar sign is used in the column you know that the unit is dollars not pounds or yen by the sign. Scales and measurement theory are a whole separate topic and are discussed in detail in Chapter 4. Abbreviation Encoding Abbreviation codes shorten the attribute values to fit into less storage space but the reader easily understands them. The codes can be either of fixed length or of variable length but computer people tend to prefer fixed length. The most common example is the two-letter postal state abbreviations . CA for California AL for Alabama which replaced the old variable-length abbreviations Calif. for .

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