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11.6 Choosing the Right Type for a Column
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For optimum storage, you should try to use the most precise type in all
cases. For example, if an integer column is used for values in the
range from `1' to `99999', `MEDIUMINT UNSIGNED' is the best type. Of
the types that represent all the required values, this type uses the
least amount of storage.
Tables created in MySQL 5.0.3 and above uses a new storage format for
`DECIMAL' columns. All basic calculation (`+,-,*,/') with `DECIMAL'
columns are done with precision of 65 decimal (base 10) digits. See
numeric-type-overview.
Calculations on `DECIMAL' values are performed using double-precision
operations. If accuracy is not too important or if speed is the highest
priority, the `DOUBLE' type may 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 64-bit integers and then convert
results back to floating-point values as necessary.
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