SQL Data Types

1. What are SQL Data Types?

SQL data types specify the kind of values that can be stored in a column, such as numbers, characters, or dates.

• Control data storage
• Ensure valid data entry
• Improve database performance

2. Categories of SQL Data Types

• Numeric Data Types
• Character/String Data Types
• Date & Time Data Types
• Boolean Data Types

3. BIT Data Type

The BIT data type stores binary values (0 or 1). It is mainly used to represent flags.

IsActive BIT

• Stores 0 or 1
• Uses very little storage

4. BOOLEAN Data Type

The BOOLEAN data type stores TRUE or FALSE values. (Some DBMS internally store it as 0 and 1.)

IsVerified BOOLEAN

5. CHAR Data Type

The CHAR data type stores fixed-length character strings.

Gender CHAR(1)

• Fixed length
• Faster access
• Wastes space if data is shorter

6. VARCHAR Data Type

The VARCHAR data type stores variable-length character strings.

Name VARCHAR(50)

• Saves storage space
• Most commonly used string type

7. DATE Data Type

The DATE data type stores date values in YYYY-MM-DD format.

DOB DATE

• Stores only date
• No time component

8. DATETIME Data Type

The DATETIME data type stores both date and time.

CreatedAt DATETIME

• Stores date and time
• Used for logs and transactions

9. DECIMAL Data Type

The DECIMAL data type stores exact numeric values with precision.

Salary DECIMAL(10,2)

• Accurate for financial data
• Avoids rounding errors

10. Example Table Using Data Types

CREATE TABLE employee (
    EmpID INT PRIMARY KEY,
    Name VARCHAR(50),
    Gender CHAR(1),
    Salary DECIMAL(10,2),
    IsActive BOOLEAN,
    JoinDate DATE,
    CreatedAt DATETIME
);

11. CHAR vs VARCHAR

CHAR                          VARCHAR
---------------------------   ---------------------------
Fixed length                  Variable length
Faster access                 Saves storage
May waste space               No space wastage

Practice Questions

1. What are SQL data types?
2. Differentiate CHAR and VARCHAR.
3. What is the use of DECIMAL data type?
4. Explain DATE and DATETIME.
5. What is BIT data type?

Practice Task