BIT vs. TINYINT: Choosing the Right Data Type for Your MySQL Booleans

1. Storage size:

   • BIT: Stores a single binary digit (0 or 1), using 1 bit of space.
   • TINYINT: Stores a small integer value, ranging from -128 to 127 (signed) or 0 to 255 (unsigned), using 1 byte (8 bits) of space.

2. Allowed values:

   • BIT: Restricted to only 0 and 1.
   • TINYINT: Accommodates a wider range of integer values, including negative numbers for the signed variant.

3. Purpose:

   • BIT: Primarily used for representing Boolean (true/false) flags, individual bits in bitfields, or storing single-bit status information.
   • TINYINT: More versatile, suitable for storing small numerical values within the defined range.

Choosing the right data type:

• For single-bit Boolean values: Use BIT(1) or BOOL (a synonym for TINYINT(1)). It's the most space-efficient and explicit choice.
• For small integers (-128 to 127 / 0 to 255): Use TINYINT if the values fall within its range. It's suitable for storing quantities, small flags, or other integer data.

Additional considerations:

• While BIT(1) and TINYINT(1) occupy the same amount of space in MySQL (1 byte), BIT is generally preferred for representing boolean values due to its explicit purpose and potential space savings when storing multiple bit flags in a single byte.
• Avoid BIT for storing values other than 0 or 1: Attempting to insert invalid values will result in errors.
• MySQL also offers a broader range of numeric data types (SMALLINT, INT, BIGINT) for larger integer values.

Here's an illustrative example:

CREATE TABLE user_flags (
  user_id INT PRIMARY KEY,
  is_active BIT(1) NOT NULL DEFAULT 0,
  is_admin TINYINT UNSIGNED NOT NULL DEFAULT 0,
  score SMALLINT NOT NULL DEFAULT 0
);

In this example:

• is_active uses BIT(1) to efficiently store a true/false flag.
• is_admin uses TINYINT UNSIGNED for a non-negative flag value (0 for not admin, 1 for admin).
• score uses SMALLINT to accommodate potentially larger integer values.

This approach is the most commonly used and generally recommended method. It offers good readability and simplicity:

CREATE TABLE user_accounts (
  user_id INT PRIMARY KEY,
  is_active BOOL NOT NULL DEFAULT 0,
  ... other columns
);

Using a custom enumeration type (MySQL 8.0+):

This option allows you to define a more descriptive type for your Boolean value:

CREATE TABLE user_accounts (
  user_id INT PRIMARY KEY,
  is_active ENUM('inactive', 'active') NOT NULL DEFAULT 'inactive',
  ... other columns
);

Using an integer field with custom logic (not recommended):

While technically possible, it's generally discouraged due to potential confusion and maintenance issues:

CREATE TABLE user_accounts (
  user_id INT PRIMARY KEY,
  is_active INT NOT NULL DEFAULT 0,
  ... other columns
);

-- Custom logic in your application code:
if (is_active == 0) {
  // User is inactive
} else {
  // User is active
}

• For most cases, using BOOL is the best option due to its simplicity, widespread usage, and clarity.
• Consider using an enumeration type (MySQL 8.0+) if you need more descriptive labels for your Boolean values (e.g., "inactive" vs. "active").
• Avoid using a custom integer field as it can lead to code complexity and potential misunderstandings.