SELECT
customerNumber, customerName
FROM
customers
WHERE
EXISTS( SELECT
1
FROM
orders
WHERE
orders.customernumber = customers.customernumber);
SELECT
customerNumber, customerName
FROM
customers
WHERE
NOT EXISTS( SELECT
1
FROM
orders
WHERE
orders.customernumber = customers.customernumber);
SELECT
employeenumber, firstname, lastname, extension
FROM
employees
WHERE
EXISTS( SELECT
1
FROM
offices
WHERE
city = 'San Francisco'
AND offices.officeCode = employees.officeCode);
SELECT
*
FROM
customers_archive;
SELECT
customerNumber, customerName
FROM
customers
WHERE
customerNumber IN (SELECT
customerNumber
FROM
orders);
SELECT
customerNumber, customerName
FROM
customers
WHERE
customerNumber IN (SELECT
customerNumber
FROM
orders);
SELECT
employeenumber, firstname, lastname
FROM
employees
WHERE
officeCode IN (SELECT
officeCode
FROM
offices
WHERE
offices.city = 'San Francisco');