How to Choose Data Types in MySQL

How do I select the right data types in MySQL?

Data types specify how MySQL stores, validates, and manipulates column values during table creation and updates.

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Description

Why do MySQL data types matter?

Picking the right data type optimizes storage, speeds up queries, and prevents invalid data from entering your tables. Wrong choices lead to wasted space and casting overhead.

Which numeric data type should I use?

Use TINYINT, SMALLINT, INT, or BIGINT for whole numbers depending on range.Choose DECIMAL(p,s) for money to avoid rounding, and FLOAT/DOUBLE only when minor precision loss is acceptable.

Example

total_amount DECIMAL(10,2) stores up to 99999999.99 without floating-point errors.

How do I store dates and times?

Use DATE for calendar dates, DATETIME for timestamps independent of time zone, and TIMESTAMP when you need automatic UTC conversion.

Example

order_date DATETIME DEFAULT CURRENT_TIMESTAMP captures order time in local server time.

When are string types better?

Use CHAR(n) for fixed-length codes (e.g., country ISO), VARCHAR(n) for variable text, and TEXT for long descriptions.Keep VARCHAR length close to expected max to save memory.

Example

email VARCHAR(255) UNIQUE handles all RFC-valid emails.

How to handle JSON and enums?

JSON columns let you store flexible attributes with built-in validation. ENUM enforces a controlled list of values while remaining space-efficient.

Example

status ENUM('pending','paid','shipped','cancelled') restricts order status to valid states.

Best practices for choosing data types?

1. Match the smallest range that fits. 2. Prefer UNSIGNED when negatives are impossible. 3. Index only columns with selective values. 4.Use NOT NULL plus sensible defaults to avoid NULL handling overhead.

What are common data type pitfalls?

Storing currency in FLOAT, using overly large VARCHAR limits, and forgetting time-zone effects with TIMESTAMP lead to subtle bugs.

Why How to Choose Data Types in MySQL is important

How to Choose Data Types in MySQL Example Usage


CREATE TABLE Orders (
    id INT UNSIGNED PRIMARY KEY AUTO_INCREMENT,
    customer_id INT UNSIGNED NOT NULL,
    order_date DATETIME DEFAULT CURRENT_TIMESTAMP,
    total_amount DECIMAL(10,2) NOT NULL,
    status ENUM('pending','paid','shipped','cancelled') DEFAULT 'pending',
    INDEX (customer_id)
);

-- Insert using correct data types
INSERT INTO Orders (customer_id, total_amount)
VALUES (1, 57.95);

How to Choose Data Types in MySQL Syntax


-- Numeric
auth_id INT UNSIGNED PRIMARY KEY,
price DECIMAL(10,2) NOT NULL,
stock SMALLINT UNSIGNED DEFAULT 0,

-- String
auth_token CHAR(32) NOT NULL,
name VARCHAR(100) NOT NULL,

-- Date & Time
created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,

-- JSON, ENUM
attributes JSON,
status ENUM('pending','paid','shipped','cancelled')

Common Mistakes

Using FLOAT for money: FLOAT introduces rounding errors. Fix by switching to DECIMAL(precision,scale) for exact arithmetic.
Oversizing VARCHAR fields: VARCHAR(10000) wastes memory and slows indexes. Estimate realistic max length and cap accordingly, e.g., VARCHAR(255) for emails.