Explain the purpose of the DISTINCT keyword in SQL and provide an example.

Question

Aryan Kumar · Answer

Sure. The DISTINCT keyword in SQL is used to remove duplicate rows from the result set of a SELECT statement. For example, let's say we have a table called
products with the following columns:
product_id (integer)product_name (string)price (decimal)
If we run the following SELECT statement:
SQL
SELECT * FROM products;
The result set will contain all of the rows in the products table, including any duplicate rows.
To remove the duplicate rows, we can use the DISTINCT keyword:
SQL
SELECT DISTINCT product_name FROM products;
This will return a result set that contains only the unique product names from the
products table.
Here is another example. Let's say we have two tables, customers and
orders:
SQL
CREATE TABLE customers (
  id INT NOT NULL AUTO_INCREMENT,
  name VARCHAR(255) NOT NULL,
  email VARCHAR(255) NOT NULL,
  PRIMARY KEY (id)
);
CREATE TABLE orders (
  id INT NOT NULL AUTO_INCREMENT,
  customer_id INT NOT NULL,
  order_date DATETIME NOT NULL,
  total_amount DECIMAL(10,2) NOT NULL,
  PRIMARY KEY (id),
  FOREIGN KEY (customer_id) REFERENCES customers (id)
);
We can use the DISTINCT keyword to combine the results of a SELECT statement that queries the
customers table with a SELECT statement that queries the orders table, and remove any duplicate rows:
SQL
SELECT DISTINCT customers.name, orders.order_date
FROM customers
INNER JOIN orders
ON customers.id = orders.customer_id;
This will return a result set that contains the unique names of all customers who have placed orders, along with the date of their most recent order.

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Explain the purpose of the DISTINCT keyword in SQL and provide an example.

Revati S Misra

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