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The following mainly brings you the practical application operation of MySQL data floating point type. I hope these contents can bring you practical use, which is also the main purpose of this article when I edit the practical application operation of MySQL data floating point type. All right, don't talk too much nonsense, let's just read the following.

1. Background

* the floating point types supported by MySQL include single precision type (float), double precision type (double), and high precision type (decimal). It is recommended to use high precision type (decimal) in digital currency types.

* MySQL floating-point and fixed-point types can be represented by the type name plus (MMagneD). M represents the total length of the value, D represents the length after the decimal point, and M and D are also known as precision and scaling. For example, float (7Power4) can be displayed as-999.9999 when saving MySQL values. If 999.00009 is inserted, the result is 999.0001. When FLOAT and DOUBLE do not specify precision, the default is displayed according to the actual precision, while when DECIMAL does not specify precision, the default integer is 10 and the decimal is 0.

two。 The range of storage and values required for integer types

Type occupies space accuracy FLOAT4 single precision to 7 decimal places after decimal point DOUBLE8 double precision to 15 decimal places DECIMAL variable length high precision to 65 decimal places

3. M / G * G (! = | =) (not necessarily equal to) M in floating point applications

M = 3.1415 G = 2.1542, unified to 6 decimal places

* single precision (float) application

* create float_test table

Mysql > CREATE TABLE float_test (- > m FLOAT (10Power6),-> g FLOAT (10L6)->) ENGINE=INNODB CHARSET=utf8mb4;Query OK, 0 rows affected (0.06 sec)

* insert m and g data

Mysql > INSERT INTO float_test SELECT 3.1415 2.1542 * Records: 1 Duplicates: 0 Warnings: 0mysql > select * from float_test +-+-+ | m | g | +-+-+ | 3.141500 | 2.154200 | +-+-+ 1 row in set (2.154200 sec)

* perform M / G * G operations

Mysql > SELECT m / g * g, m FROM float_test;+-+-+ | m / g * g | m | +-+-+ | 3.1414999962 | 3.141500 | +-+-+ 1 row in set (sec)

* double precision (double) application

* create double_test table

Mysql > CREATE TABLE double_test (- > m DOUBLE (10Power6),-> g DOUBLE (10L6)->) ENGINE=INNODB CHARSET=utf8mb4;Query OK, 0 rows affected (0.08 sec)

* insert m and g data

Mysql > INSERT INTO double_test SELECT 3.1415 2.1542 * Records: 1 Duplicates: 0 Warnings: 0mysql > select * from double_test +-+-+ | m | g | +-+-+ | 3.141500 | 2.154200 | +-+-+ 1 row in set (2.154200 sec)

* perform M / G * G operations

Mysql > SELECT m / g * g, m FROM double_test;+-+-+ | m / g * g | m | +-+-+ | 3.1415000000 | 3.141500 | +-+-+ 1 row in set (sec)

* High precision (decimal) applications

* create decimal_test table

Mysql > CREATE TABLE decimal_test (- > m DECIMAL (10 sec 6),-> g DECIMAL (10 rows affected 6)->) ENGINE=INNODB CHARSET=utf8mb4;Query OK, 0 rows affected (0.05 sec)

* insert m and g data

Mysql > INSERT INTO decimal_test SELECT 3.1415 2.1542 * Records: 1 Duplicates: 0 Warnings: 0mysql > SELECT * FROM decimal_test +-+-+ | m | g | +-+-+ | 3.141500 | 2.154200 | +-+-+ 1 row in set (2.154200 sec)

* perform M / G * G operations

Mysql > SELECT m / g * g, m FROM decimal_test +-+ | m / g * g | m | +-+ | 3.1415000000000000 | 3.141500 | +-+-+ 1 row in set (0.00 sec)

4. Summary of floating-point type application

* if the floating point number does not write precision and scale, it will be displayed according to the actual situation.

* if there is precision and scale, the data will be rounded and inserted, and the system will not report an error.

* if DECIMAL does not set precision and scale, it just operates in accordance with the default (10d0). If the data exceeds the precision and scale value, an error will be reported.

* accounts and accounting systems must use DECIMAL types to determine accuracy and financial security.

5. Summary

In order to demand-driven technology, there is no difference in technology itself, only in business.

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