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MySQL uses DISTINCT to filter duplicate data

The DISTINCT keyword in MySQL is used to return unique (distinct) values in the result set of a SELECT statement. It eliminates all the duplicate records and fetches only the unique ones.

Here's a basic usage of the DISTINCT keyword:

SELECT DISTINCT column_name FROM table_name;

For example, consider a table called employees with a column department_id. If you want to get a list of all unique departments in which employees work, you could use the DISTINCT keyword like this:

SELECT DISTINCT department_id FROM employees;

This query will return a list of unique department_id values from the employees table.

If you want to select distinct values across multiple columns, you can include all the column names in your SELECT statement. For example:

SELECT DISTINCT department_id, job_title FROM employees;

This query will return all unique combinations of department_id and job_title.

Important Note: When used with multiple columns, the DISTINCT keyword will consider the combination of all the columns when determining the uniqueness of a record. For example, in the above query, a department with the same department_id but different job_title would be considered a unique combination and included in the result set.

Also, NULL is considered a distinct value. If a column has NULL values, each NULL is considered distinct from the others, so a SELECT DISTINCT query on that column would return one NULL.

MySQL DISTINCT keyword example:
- Description: The DISTINCT keyword is used to retrieve unique values from a specified column or combination of columns in a result set.
- Example:
```
SELECT DISTINCT column_name FROM your_table;
```
How to use DISTINCT in MySQL:
- Description: Use the DISTINCT keyword in a SELECT statement to filter and return unique values.
- Example:
```
SELECT DISTINCT product_category FROM products;
```
Removing duplicates with DISTINCT in MySQL:
- Description: DISTINCT eliminates duplicate values from the result set, providing only unique values.
- Example:
```
SELECT DISTINCT employee_department FROM employees;
```
Filtering unique values using DISTINCT in MySQL:
- Description: Apply DISTINCT to filter out duplicate values and return only unique values.
- Example:
```
SELECT DISTINCT city FROM customers;
```
Distinct values in a specific column in MySQL:
- Description: Use DISTINCT to retrieve unique values from a specific column in a MySQL table.
- Example:
```
SELECT DISTINCT order_status FROM orders;
```
Applying DISTINCT to multiple columns in MySQL:
- Description: Combine multiple columns in the DISTINCT clause to retrieve unique combinations of values.
- Example:
```
SELECT DISTINCT first_name, last_name FROM employees;
```
Counting distinct values with MySQL DISTINCT:
- Description: Use COUNT(DISTINCT column_name) to count the number of unique values in a specific column.
- Example:
```
SELECT COUNT(DISTINCT product_category) AS UniqueCategories FROM products;
```
Examples of using DISTINCT in MySQL queries:
- Description: Demonstrate various use cases of the DISTINCT keyword in MySQL queries.
- Examples:
```
SELECT DISTINCT customer_type FROM customers;
SELECT DISTINCT city, country FROM addresses;
```