Data types in SQL

What Are Data Types?

Each column must be assigned a data type, such as:

Data Type	Description	Usage Example in a Table
CHAR	string(0-255), can store characters of fixed length. Eg: Alice, all 50 is reserved here. Extra memory is wasted after storing ‘Alice’	CHAR(50)
VARCHAR(n)	string (0-255), can store characters up to given length.	VARCHAR(50)
BLOB	string (0-65535), can store binary large object.	BLOB(1000)
INT	Standard integer (usually 4 bytes). Can store whole numbers.	age INT, salary INT
TINYINT	Very small integer (1 byte). Range: 0 to 255 (unsigned) or -128 to 127 (signed).	is_active TINYINT → use as boolean (0 or 1)
BIGINT	Large integer (8 bytes). Use for values exceeding INT range.	user_id BIGINT for large ID systems
BIT(n)	Stores n bits (1s and 0s). Common for flags or binary data.	flags BIT(4) → stores 4-bit binary value
FLOAT	Decimal number, with precision to 23 digits.	temperature FLOAT
DOUBLE	Decimal number, with precision to 24 - 53 digits.	account_balance DOUBLE
BOOLEAN	Boolean values 0 or 1.	BOOLEAN
DATE	Stores a calendar date (YYYY-MM-DD) ranging from 1000-01-01 to 9999-12-31	birth_date DATE
YEAR	Stores only the year (e.g., 2023). Range: 1901 to 2155	enrollment_year YEAR

In SQL (especially in MySQL), numeric data types like INT, TINYINT, BIGINT, etc., can be either:

SIGNED – can store both positive and negative numbers
UNSIGNED – can store only positive numbers (and zero), but with a larger positive range

By default, numeric types are SIGNED unless you explicitly declare them as UNSIGNED.

Use UNSIGNED when:

Term	Stores	Use When…
SIGNED	Positive & negative	You expect negative values (e.g., temperature, balance)
UNSIGNED	Only positive (more range)	IDs, counters, quantities, prices, etc.