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NOTE on price DEC(5,2)

The DEC(5,2) in the column definition price DEC(5,2) NOT NULL is used to specify a decimal (fixed-point) data type with precision and scale. Here’s a breakdown of what DEC(5,2) means:

  • DEC: Stands for DECIMAL, a numeric data type used to store exact numeric values with decimal points.
  • (5,2):
    • Precision (5): The total number of digits that can be stored, both to the left and right of the decimal point.
    • Scale (2): The number of digits that can be stored to the right of the decimal point.

Example

For DEC(5,2):

  • Total digits: 5
  • Digits to the right of the decimal point: 2

This means the price column can store numbers ranging from -999.99 to 999.99. The total number of digits, including those before and after the decimal point, cannot exceed 5, and exactly 2 digits will be stored after the decimal point.

Purpose

The purpose of using DEC(5,2) for the price column is to:

  1. Ensure Precision: Store exact monetary values with two decimal places, which is common for prices to represent cents.
  2. Limit Range: Constrain the range of values that the price column can hold, ensuring values are within a sensible and expected range for pricing items.

Full Table Definition

Here’s the complete table definition for reference:

sqlCopy code
CREATE TABLE cart_items (
    item_id INT AUTO_INCREMENT PRIMARY KEY,
    name VARCHAR(255) NOT NULL,
    quantity INT NOT NULL,
    price DEC(5,2) NOT NULL,
    sales_tax DEC(5,2) NOT NULL DEFAULT 0.1,
    CHECK(quantity > 0),
    CHECK(sales_tax >= 0)
);

Summary

The DEC(5,2) ensures that the price column in the cart_items table can store values with up to 5 digits in total, with 2 digits after the decimal point, providing precision and control over the range of values stored.