CREATE INDEX customers_user_name_idx ON customers (user_name);

CREATE INDEX customers_last_name_first_name_idx ON customers (last_name, first_name);

DROP INDEX IF EXISTS customers_city_idx;

SELECT
    c.first_name,
    c.last_name,
    COUNT(o.order_id) AS NumOforders
FROM customers       AS c
INNER JOIN orders    AS o    
ON o.customer_id = c.customer_id
WHERE c.last_name IN ('Smith', 'Jones')
GROUP BY c.first_name, c.last_name;

CREATE INDEX users_user_name_internal_idx ON users (user_name)
WHERE email_address LIKE '%@wellsfargo.com';

CREATE INDEX logins_date_time_idx ON logins (date_time DESC, user_name);

To cluster your database table using an existing index (say products_product_name_idx) on the products table you would use:

CLUSTER products USING products_product_name_idx;
 
If you have already established what index should be clustered on you can simply tell the system which table to apply the cluster on.

CLUSTER products;
 
And if you want to cluster every table in your database that has an identified index to use you can simply call

CLUSTER;

CREATE UNIQUE INDEX unique_manufacture_company_name_idx ON manufacture(LOWER(company_name));