> ## Documentation Index
> Fetch the complete documentation index at: https://rajanand.org/llms.txt
> Use this file to discover all available pages before exploring further.

# Creating and Modifying Tables

> Create, alter and drop tables

Tables are the building blocks of a database, storing data in a structured format. In this article, we’ll explore how to create and alter tables.

### What Is a Table?

A table is a collection of rows and columns. Each column represents a specific data field (e.g., name, age), while each row represents a single record. Designing tables effectively is critical for managing your data efficiently.

#### Basic Syntax for Creating Tables

The `CREATE TABLE` statement defines the structure of a table, specifying column names, data types, and optional constraints.

```sql theme={"system"}
CREATE TABLE employees (
    employee_id INT PRIMARY KEY,
    first_name VARCHAR(50) NOT NULL,
    last_name VARCHAR(50) NOT NULL,
    hire_date DATE,
    salary DECIMAL(10, 2) CHECK (salary > 0)
);
```

### Adding Data to a Table

Once your table is created, use the `INSERT INTO` statement to populate it with data like you did in the [previous article](working-with-data.md).

```sql theme={"system"}
INSERT INTO employees (employee_id, first_name, last_name, hire_date, salary)
VALUES (1, 'John', 'Doe', '2023-05-01', 55000.00);
```

### Viewing Table Structure

To understand a table’s structure, you can use database-specific commands.

```sql theme={"system"}
EXEC sp_help 'employees';
```

### Altering Table

The `ALTER TABLE` statement lets you modify an existing table by adding, altering, or dropping columns.

#### **Adding a Column**

```sql theme={"system"}
ALTER TABLE employees
ADD department VARCHAR(50);
```

#### **Modifying a Column**

```sql theme={"system"}
ALTER TABLE employees
ALTER COLUMN salary DECIMAL(12, 2);
```

**Dropping a Column**

```sql theme={"system"}
ALTER TABLE employees
DROP COLUMN department;
```

### Deleting a Table

If a table is no longer needed, you can delete it using the `DROP TABLE` statement. Be careful, as this 

<Warning>
  `DROP TABLE` permanently removes the table and its data.
</Warning>

```sql theme={"system"}
DROP TABLE employees;
```

#### Key Takeaways

* The `CREATE TABLE` statement is used to define a table’s structure, including columns and their data types.
* Use `ALTER TABLE` to make changes to an existing table—add, modify, or drop columns.
* Always double-check before using `DROP TABLE`, as it removes the table and all the data.

Next, we’ll explore how to establish [**relationships between tables**](/sql/relationships-between-tables) using foreign keys. This will help you connect data effectively across your database.