Chapter 05 - Exercises

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-- TK 70-461 - Chapter 05 - Grouping and Windowing
-- Exercises
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-- Lesson 01 - Writing Grouped Queries
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-- Practice - Writing Grouped Queries
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-- Exercise 1 - Aggregate Information About Customer Orders
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-- 2.
-- compute number of orders per customer for customers from Spain
USE TSQL2012;
SELECT C.custid, COUNT(*) AS numorders
FROM Sales.Customers AS C
INNER JOIN Sales.Orders AS O
ON C.custid = O.custid
WHERE C.country = N'Spain'
GROUP BY C.custid;
-- 3.
-- add city to the SELECT list
SELECT C.custid, C.city, COUNT(*) AS numorders
FROM Sales.Customers AS C
INNER JOIN Sales.Orders AS O
ON C.custid = O.custid
WHERE C.country = N'Spain'
GROUP BY C.custid;
-- 4.
-- add city to GROUP BY as well
SELECT C.custid, C.city, COUNT(*) AS numorders
FROM Sales.Customers AS C
INNER JOIN Sales.Orders AS O
ON C.custid = O.custid
WHERE C.country = N'Spain'
GROUP BY C.custid, C.city;
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-- Exercise 2 - Define Multiple Grouping Sets
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-- 1.
-- add total of all orders; present detail first
SELECT C.custid, C.city, COUNT(*) AS numorders
FROM Sales.Customers AS C
INNER JOIN Sales.Orders AS O
ON C.custid = O.custid
WHERE C.country = N'Spain'
GROUP BY GROUPING SETS ( (C.custid, C.city), () )
ORDER BY GROUPING(C.custid);
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-- Lesson 02 - Pivoting and Unpivoting Data
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-- Practice - Pivoting Data
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-- Exercise 1 - Pivot Data Using a Table Expression
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-- 2.
-- attempt to return maximum shipping date for each order year and shipper ID
-- with order years on rows and shipper IDs (1, 2 and 3) on columns
SELECT YEAR(orderdate) AS orderyear, [1], [2], [3]
FROM Sales.Orders
PIVOT( MAX(shippeddate) FOR shipperid IN ([1],[2],[3]) ) AS P;
-- 3.
-- correct the query from step 2 to return only one row per order year
-- by using a table expression
WITH PivotData AS
(
SELECT YEAR(orderdate) AS orderyear, shipperid, shippeddate
FROM Sales.Orders
)
SELECT orderyear, [1], [2], [3]
FROM PivotData
PIVOT( MAX(shippeddate) FOR shipperid IN ([1],[2],[3]) ) AS P;
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-- Exercise 2 - Pivot Data and Compute Counts
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-- 1.
-- show customer IDs on rows, shipper IDs on columns, count of orders in intersection
-- first attempt to use a query similar to the one in the module, but with COUNT(*)
WITH PivotData AS
(
SELECT
custid , -- grouping column
shipperid -- spreading column
FROM Sales.Orders
)
SELECT custid, [1], [2], [3]
FROM PivotData
PIVOT( COUNT(*) FOR shipperid IN ([1],[2],[3]) ) AS P;
-- 2.
-- solve the problem by either returning the key or a dummy column
WITH PivotData AS
(
SELECT
custid , -- grouping column
shipperid, -- spreading column
1 AS aggcol -- aggregation column
FROM Sales.Orders
)
SELECT custid, [1], [2], [3]
FROM PivotData
PIVOT( COUNT(aggcol) FOR shipperid IN ([1],[2],[3]) ) AS P;
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-- Lesson 03 - Using Window Functions
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-- Practice - Using Window Functions
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-- Exercise 1 - Use Window Aggregate Functions
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-- 2.
-- per each customer and order compute moving average value of the customer's last three orders
SELECT custid, orderid, orderdate, val,
AVG(val) OVER(PARTITION BY custid
ORDER BY orderdate, orderid
ROWS BETWEEN 2 PRECEDING
AND CURRENT ROW) AS movingavg
FROM Sales.OrderValues;
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-- Exercise 2 - Using Window Ranking and Offset Functions
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-- 1.
-- filter for each shipper the three orders with the highest freight
WITH C AS
(
SELECT shipperid, orderid, freight,
ROW_NUMBER() OVER(PARTITION BY shipperid
ORDER BY freight DESC, orderid) AS rownum
FROM Sales.Orders
)
SELECT shipperid, orderid, freight
FROM C
WHERE rownum <= 3
ORDER BY shipperid, rownum;
-- 2.
-- compute the difference between the current order value and the value of the customer's previous order,
-- as well as the difference between the current order value and the value of the customer's next order
SELECT custid, orderid, orderdate, val,
val - LAG(val) OVER(PARTITION BY custid
ORDER BY orderdate, orderid) AS diffprev,
val - LEAD(val) OVER(PARTITION BY custid
ORDER BY orderdate, orderid) AS diffnext
FROM Sales.OrderValues;