- 10 Data Types
- 10.1 Data Type Overview
- 10.2 Numeric Types
- 10.3 Date and Time Types
- 10.4 String Types
- 10.5 Data Type Storage Requirements
- 10.6 Choosing the Right Type for a Column
- 10.7 Using Data Types from Other Database Engines
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 use a new storage format
for DECIMAL columns. All basic
calculations (+, -,
*, and /) with
DECIMAL columns are done with
precision of 65 decimal (base 10) digits. See
Section 10.1.1, “Overview of Numeric Types”.
Prior to MySQL 5.0.3, 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.
PROCEDURE ANALYSE can be used to obtain
suggestions for optimal column data types. For more information,
see Section 21.3.1, “PROCEDURE ANALYSE”.
User Comments
Instead of
"For the most efficient use of storage, try to use the MOST precise type in all cases."
I think it should be
"For the most efficient use of storage, try to use the LEAST precise type THAT WILL ACCOMMODATE ALL POSSIBLE VALUES in all cases."
(EMPHASIS made just to highlight the difference.)
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