Summary: in this tutorial, you will learn about MySQL DECIMAL data type and how to use it to store exact numeric values in the databases.

Introduction to MySQL DECIMAL data type

The MySQL DECIMAL data type allows you to store exact numeric values in the database. In practice, you often use the DECIMAL data type for columns that preserve exact precision e.g., monetary data in financial systems.

To define a column whose data type is DECIMAL, you use the following syntax:

column_name DECIMAL(P,D);Code language: SQL (Structured Query Language) (sql)

In this syntax:

• P is the precision that represents the number of significant digits. The range of P is 1 to 65.
• D is the scale that represents the number of digits after the decimal point. The range of D is 0 and 30. MySQL requires that D is less than or equal to (<=) P.

The DECIMAL(P,D) means that the column can store up to P digits with D decimals. The actual range of the decimal column depends on the precision and scale.

Besides the DECIMAL keyword, you can also use DEC, FIXED, or NUMERIC because they are synonyms for DECIMAL.

The following example defines the amount column with DECIMAL data type.

amount DECIMAL(6,2);Code language: SQL (Structured Query Language) (sql)

In this example, the amount column can store 6 digits with 2 decimal places; therefore, the range of the amount column is from 9999.99 to -9999.99.

MySQL allows you to use the following syntax:

column_name DECIMAL(P);Code language: SQL (Structured Query Language) (sql)

This is equivalent to:

column_name DECIMAL(P,0);Code language: SQL (Structured Query Language) (sql)

In this case, the column contains no fractional part or decimal point.

In addition, you can even use the following syntax:

column_name DECIMAL;Code language: SQL (Structured Query Language) (sql)

The default value of P is 10 and D is 0, which is equivalent to the following:

column_name DECIMAL(10,0);

MySQL DECIMAL storage

MySQL assigns the storage for integer and fractional parts separately. MySQL uses a binary format to store the DECIMAL values. It packs 9 digits into 4 bytes.

For each part, it takes 4 bytes to store each multiple of 9 digits. The storage required for leftover digits is illustrated in the following table:

For example, DECIMAL(19,9) has 9 digits for the fractional part and 19-9 = 10 digits for the integer part. The fractional part requires 4 bytes. The integer part requires 4 bytes for the first 9 digits, for 1 leftover digit, it requires 1 more byte. In total, the DECIMAL(19,9) column requires 9 bytes.

MySQL DECIMAL data type and monetary data

We often use the DECIMAL data type for monetary data such as prices, salary, account balances, and so on. If you design a database that handles the monetary data, the following syntax should be fine.

amount DECIMAL(19,2);Code language: SQL (Structured Query Language) (sql)

However, if you want to comply with Generally Accepted Accounting Principles (GAAP) rules, the monetary column must have at least 4 decimal places to make sure that the rounding value does not exceed $0.01. In this case, you should define the column with 4 decimal places as follows:

amount DECIMAL(19,4);Code language: SQL (Structured Query Language) (sql)

 MySQL DECIMAL data type example

First, create a new table named materials:

CREATE TABLE materials (
    id INT AUTO_INCREMENT PRIMARY KEY,
    description VARCHAR(255) NOT NULL,
    cost DECIMAL(19,4) NOT NULL
);Code language: PHP (php)

The materials table has three columns:

• id is the auto-increment primary key column with the INT data type.
• description represents the material’s description with the VARCHAR data type.
• cost represents the cost of the material, which has the DECIMAL(19,4).

The cost column can store up to 19 digits with 4 decimal places.

Second, insert data into the materials table.

INSERT INTO materials(description, cost) 
VALUES 
  ('Bicycle', 500.34), 
  ('Seat', 10.23), 
  ('Break', 5.21);Code language: SQL (Structured Query Language) (sql)

Third, query data from the materials table.

SELECT 
    *
FROM
    materials;Code language: SQL (Structured Query Language) (sql)

Output:

+----+-------------+----------+
| id | description | cost     |
+----+-------------+----------+
|  1 | Bicycle     | 500.3400 |
|  2 | Seat        |  10.2300 |
|  3 | Break       |   5.2100 |
+----+-------------+----------+
3 rows in set (0.00 sec)Code language: JavaScript (javascript)

Summary

• Use MySQL DECIMAL data type to store exact numeric values such as financial data in the database.
• Use column_name DECIMAL (P, D) to define a column with the DECIMAL data type that has up to P digits and D decimal places.
• The DECIMAL(P) is equivalent to DECIMAL(P,0) and DECIMAL is equivalent to DECIMAL(P, 0).