The DECIMAL data type in MySQL is used to store fixed-point numbers, also known as decimal numbers or exact numeric values. It is commonly employed to store monetary and financial data where precision is crucial. Unlike the FLOAT and DOUBLE data types, which are approximate numeric types, DECIMAL provides exact numeric storage with a fixed number of decimal places.

DECIMAL introduction

Here are the key characteristics and considerations for the MySQL DECIMAL data type:

Syntax
The syntax for defining a DECIMAL column in a table is as follows:

DECIMAL(M, D)

Where:

M is the total number of digits (precision), including both the integer and decimal parts.
D is the number of digits after the decimal point (scale).

Example

CREATE TABLE financial_data (
    amount DECIMAL(10, 2)
);

In this example, the “amount” column can store up to 10 digits in total, with 2 digits after the decimal point.

Precision and Scale

Precision (M): The total number of digits in the number.
Scale (D): The number of digits to the right of the decimal point.

Storage

DECIMAL is a fixed-point type, which means it stores numbers as strings.
The storage required for DECIMAL(M, D) is approximately M+2 bytes, rounded up to the nearest multiple of 4.

Arithmetic Operations

DECIMAL supports arithmetic operations with exact precision, making it suitable for financial calculations.
When performing arithmetic operations on DECIMAL values, the result’s precision and scale are determined by the operation and the input values.

Rounding

MySQL handles rounding during arithmetic operations to maintain the specified precision and scale.
It’s essential to be mindful of rounding behavior, especially when dealing with financial data.

Use Cases

DECIMAL is commonly used for storing monetary values, percentages, and other exact numeric data where precision is critical.

Performance Considerations

DECIMAL operations may have higher computational costs compared to approximate numeric types like FLOAT or DOUBLE.
It is advisable to use DECIMAL when precise representation is required, and the performance impact is acceptable.

In summary, the DECIMAL data type in MySQL is a reliable choice for storing exact numeric values, particularly in scenarios where precision and accuracy are essential, such as financial and monetary calculations. When designing database schemas, it’s crucial to choose the appropriate precision and scale for DECIMAL columns based on the specific requirements of the data being stored.