SQL-Server-Tutorial/SQL Server Subquery.sql at main · krasigarev/SQL-Server-Tutorial · GitHub

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-- IN Operator

SELECT
    order_id,
    order_date,
    customer_id
FROM sales.orders
WHERE customer_id IN (
        SELECT
            customer_id
        FROM sales.customers
        WHERE city = 'New York')
ORDER BY order_date DESC;
GO


SELECT
    product_name,
    list_price
FROM production.products
WHERE list_price > (
        SELECT
            AVG(list_price)
        FROM production.products
        WHERE brand_id IN (
            SELECT
                brand_id
            FROM production.brands
            WHERE brand_name = 'Strider' OR brand_name = 'Trek'
        )
    )
ORDER BY list_price;
GO


SELECT
    order_id,
    order_date,
    (
        SELECT
            MAX(list_price)
        FROM sales.order_items i
        WHERE i.order_id = o.order_id
    )
FROM sales.orders o
ORDER BY order_date DESC;
GO

SELECT
    product_id,
    product_name
FROM production.products
WHERE category_id IN (
        SELECT
            category_id
        FROM production.categories
        WHERE category_name = 'Mountain Bikes' OR category_name = 'Road Bikes'
    );
GO

-- ANY Operator
SELECT
    product_id,
    list_price
FROM production.products
WHERE list_price >= ANY (
        SELECT
            AVG(list_price)
        FROM production.products
        GROUP BY brand_id
    );
GO

-- ALL Operator
SELECT
    product_name,
    list_price
FROM production.products
WHERE list_price >= ALL (
        SELECT
            AVG(list_price)
        FROM production.products
        GROUP BY brand_id
    );
GO

-- EXISTS or NOT EXISTS

SELECT
    customer_id,
    first_name,
    last_name,
    city
FROM sales.customers c
WHERE EXISTS (
        SELECT
            customer_id
        FROM sales.orders o
        WHERE o.customer_id = c.customer_id AND YEAR(order_date) = 2017
    )
ORDER BY first_name, last_name;
GO

SELECT
    customer_id,
    first_name,
    last_name,
    city
FROM sales.customers c
WHERE NOT EXISTS (
        SELECT
            customer_id
        FROM sales.orders o
        WHERE o.customer_id = c.customer_id AND YEAR(order_date) = 2017
    )
ORDER BY first_name, last_name;
GO

SELECT
    AVG(order_count) average_order_count_by_staff
FROM (
    SELECT
        staff_id,
        COUNT(order_id) order_count
    FROM sales.orders
    GROUP BY staff_id
) t;