explain natural joins in dbms with examples and syntax

In a Database Management System (DBMS), a **natural join** is a type of join operation that combines rows from two or more tables based on their common columns. A natural join automatically matches columns with the same name and compatible data types from each table involved in the join. It eliminates duplicate columns from the result, retaining only one instance of each of the common columns.

### Syntax

The syntax for a natural join in SQL is as follows:

```sql
SELECT *
FROM Table1
NATURAL JOIN Table2;
```

### Key Points

1. **Common Columns**: The join is based on columns that have the same name and compatible data types in both tables.
2. **Elimination of Duplicates**: In the result set, if there are matching columns, only one instance of it appears in the output.
3. **Implicit Join Condition**: Unlike other joins (like inner join), you do not have to specify the join condition explicitly; it automatically uses all columns with the same name.
4. **Use Cases**: Natural joins are handy when dealing with tables that have common attributes and you want to combine their information directly without explicitly stating how they are related.

### Example

Let's illustrate natural joins with an example.

Assume we have the following two tables:

**Table: Employees**
| Employee_ID | Name   | Department_ID |
|-------------|--------|---------------|
| 1           | John   | 101           |
| 2           | Alice  | 102           |
| 3           | Bob    | 101           |

**Table: Departments**
| Department_ID | Department_Name |
|---------------|------------------|
| 101           | Sales            |
| 102           | Marketing        |
| 103           | HR               |

Now, we can perform a natural join between the `Employees` and `Departments` tables based on the `Department_ID`.

### SQL Query

```sql
SELECT *
FROM Employees
NATURAL JOIN Departments;
```

### Result

The result of the above query will be:

| Employee_ID | Name   | Department_Name |
|-------------|--------|------------------|
| 1           | John   | Sales            |
| 3           | Bob    | Sales            |
| 2           | Alice  | Marketing        |

### Explanation of the Result

- The natural join combines the `Departments` table with the `Employees` table using the `Department_ID` column, as it is common to both tables.
- The output contains columns from both tables: `Employee_ID`, `Name`, and `Department_Name`.
- The duplicate `Department_ID` column from the result is eliminated, showing only `Department_Name`.

### Considerations

1. **Ambiguity**: If two tables have columns with the same name that are not intended to be used for the join, this can lead to unexpected results. It’s crucial to ensure that the columns being matched are correctly intended for joining.
  
2. **Join Types**: A natural join is similar to an inner join, but you need to be aware that it doesn't allow for more sophisticated conditions like outer joins (LEFT, RIGHT, FULL).

3. **Readonly Query**: Natural joins do not modify the original tables but only return a result set based on the query.

Natural joins can be powerful for quickly combining data from related tables with shared attributes, but care should be taken to ensure the joins are logical and intended.