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MySQL Tip: Use DISTINCT keyword to return only distinct (unique) values.

MySQL Tip: Use DISTINCT keyword to return only distinct (unique) values

When working with databases, it is common to encounter situations where you need to retrieve only unique values from a specific column. In MySQL, the DISTINCT keyword comes in handy for this purpose. By using the DISTINCT keyword in your queries, you can eliminate duplicate values and obtain a result set with only distinct (unique) values.

Understanding the DISTINCT keyword

The DISTINCT keyword is used in conjunction with the SELECT statement to retrieve unique values from a column or a combination of columns in a table. It instructs the database engine to eliminate duplicate rows from the result set, returning only distinct values.

Let’s consider an example to better understand how the DISTINCT keyword works. Suppose we have a table named “customers” with the following data:

+----+----------+
| ID |  Name    |
+----+----------+
| 1  | John     |
| 2  | Mary     |
| 3  | John     |
| 4  | David    |
| 5  | Mary     |
+----+----------+

If we want to retrieve only the distinct names from the “Name” column, we can use the following query:

SELECT DISTINCT Name FROM customers;

The result of this query would be:

+----------+
|  Name    |
+----------+
| John     |
| Mary     |
| David    |
+----------+

As you can see, the duplicate names “John” and “Mary” have been eliminated, and only the distinct values are returned.

Using DISTINCT with multiple columns

The DISTINCT keyword can also be used with multiple columns to retrieve unique combinations of values. Let’s consider another example using a table named “orders” with the following data:

+----+----------+---------+
| ID |  Product |  Price  |
+----+----------+---------+
| 1  | Apple    |  1.99   |
| 2  | Orange   |  0.99   |
| 3  | Apple    |  1.99   |
| 4  | Banana   |  0.50   |
| 5  | Orange   |  0.99   |
+----+----------+---------+

If we want to retrieve only the distinct combinations of “Product” and “Price” from the “orders” table, we can use the following query:

SELECT DISTINCT Product, Price FROM orders;

The result of this query would be:

+----------+---------+
|  Product |  Price  |
+----------+---------+
| Apple    |  1.99   |
| Orange   |  0.99   |
| Banana   |  0.50   |
+----------+---------+

Again, the duplicate combinations of “Product” and “Price” have been eliminated, and only the distinct values are returned.

Conclusion

The DISTINCT keyword in MySQL is a powerful tool for retrieving only distinct (unique) values from one or more columns in a table. By using the DISTINCT keyword in your queries, you can eliminate duplicate rows and obtain a result set with only the unique values you need.

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