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Sometimes decisions about these types of cases can be made more easily by asking a simple question: Are there ever exceptions? If an exceptional case ever occurs, even just once, you must allow for it. You will find that people who talk to you about designing a database invariably think that if exceptions don't occur very often, they don't matter. When you're creating a table, you can't think that way. The question you need to ask isn't "How often do exceptions occur?" It's "Do exceptions ever occur?" If they do, you must take them into account.
What Are the Performance and Efficiency Issues?
Your choice of column type can influence query performance in several ways. If you keep the general guidelines discussed in the following sections in mind, you'll be able to choose types that will help MySQL process your tables more efficiently.
Numeric Versus String Operations
Numeric operations are generally faster than string operations. Consider comparison operations. Numbers can be compared in a single operation. String comparisons may involve several byte-by-byte or character-by-character comparisons, more so as the strings become longer.
If a string column has a limited number of values, use an ENUM or SET type to get the advantages of numeric operations. These types are represented internally as numbers and can be processed more efficiently.
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