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(mysql.info)Choosing types

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Choosing the Right Type for a Column
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For the most efficient use of storage, try to use the most precise type
in all cases. For example, if an integer column will be used for values
in the range between `1' and `99999', `MEDIUMINT UNSIGNED' is the best
type.

Accurate representation of monetary values is a common problem. In
MySQL, you should use the `DECIMAL' type. This is stored as a string,
so no loss of accuracy should occur. If accuracy is not too important,
the `DOUBLE' type may also be good enough.

For high precision, you can always convert to a fixed-point type stored
in a `BIGINT'. This allows you to do all calculations with integers and
convert results back to floating-point values only when necessary.