04 | Grouping and Aggregating Data

Querying Microsoft SQL Server 2012 Jump Start

01 | Introducing SQL Server 2012

SQL Server types of statements; other SQL statement elements; basic SELECT statements

02 | Advanced SELECT StatementsDISTINCT, Aliases, scalar functions and CASE, using JOIN and MERGE; Filtering and sorting data, NULL

values

03 | SQL Server Data Types Introduce data types, data type usage, converting data types, understanding SQL Server function types

04 | Grouping and Aggregating DataAggregate functions, GROUP BY and HAVING clauses, subqueries; self-contained, correlated, and EXISTS; Views, inline-table

valued functions, and derived tables

| Lunch Break Eat, drink, and recharge for the afternoon session

STDEV STDEVP VAR VARP

SUM MIN MAX AVG COUNT COUNT_BIG

CHECKSUM_AGG GROUPING GROUPING_ID

Common Statistical Other

UniqueOrders Avg_UnitPrice Min_OrderQty Max_LineTotal------------- ------------ ------------ -------------31465 465.0934 1 27893.619000

SELECT COUNT (DISTINCT SalesOrderID) ASUniqueOrders, AVG(UnitPrice) AS Avg_UnitPrice, MIN(OrderQty)AS Min_OrderQty, MAX(LineTotal) AS Max_LineTotalFROM Sales.SalesOrderDetail;

SELECT SalesPersonID, YEAR(OrderDate) AS OrderYear,COUNT(CustomerID) AS All_Custs,COUNT(DISTINCT CustomerID) AS Unique_CustsFROM Sales.SalesOrderHeaderGROUP BY SalesPersonID, YEAR(OrderDate);

SalesPersonID OrderYear All_Custs Unique_custs----------- ----------- ----------- ------------289 2006 84 48281 2008 52 27285 2007 9 8277 2006 140 57

SELECT FROM WHERE GROUP BY ;

SELECT SalesPersonID, COUNT(*) AS CntFROM Sales.SalesOrderHeaderGROUP BY SalesPersonID;

Logical Order Phase Comments

5 SELECT

1 FROM

2 WHERE

3 GROUP BY Creates groups

4 HAVING Operates on groups

6 ORDER BY

SELECT productid, MAX(OrderQty) AS largest_orderFROM Sales.SalesOrderDetailGROUP BY productid;

SELECT CustomerID, COUNT(*) AS cntFROM Sales.SalesOrderHeaderGROUP BY CustomerID;

SELECT CustomerID, COUNT(*) ASCount_OrdersFROM Sales.SalesOrderHeaderGROUP BY CustomerIDHAVING COUNT(*) > 10;

Using a COUNT(*) expression in HAVING clause is useful to solve common business problems:

Show only customers that have placed more than one order:

Show only products that appear on 10 or more orders:

SELECT Cust.Customerid, COUNT(*) AS cntFROM Sales.Customer AS CustJOIN Sales.SalesOrderHeader AS Ord ON Cust.CustomerID = ORD.CustomerIDGROUP BY Cust.CustomerIDHAVING COUNT(*) > 1;

SELECT Prod.ProductID, COUNT(*) AS cntFROM Production.Product AS ProdJOIN Sales.SalesOrderDetail AS Ord ON Prod.ProductID = Ord.ProductIDGROUP BY Prod.ProductIDHAVING COUNT(*) >= 10;

Working with subqueries

Writing scalar subqueries

SELECT SalesOrderID, ProductID, UnitPrice, OrderQtyFROM Sales.SalesOrderDetailWHERE SalesOrderID = (SELECT MAX(SalesOrderID) AS LastOrderFROM Sales.SalesOrderHeader);

Writing multi-valued subqueries

SELECT CustomerID, SalesOrderId,TerritoryIDFROM Sales.SalesorderHeaderWHERE CustomerID IN (SELECT CustomerIDFROM Sales.CustomerWHERE TerritoryID = 10);

Writing queries using EXISTS with subqueries

SELECT CustomerID, PersonIDFROM Sales.Customer AS CustWHERE EXISTS (SELECT * FROM Sales.SalesOrderHeader AS OrdWHERE Cust.CustomerID = Ord.CustomerID);

SELECT CustomerID, PersonIDFROM Sales.Customer AS CustWHERE NOT EXISTS (SELECT * FROM Sales.SalesOrderHeader AS OrdWHERE Cust.CustomerID = Ord.CustomerID);

CREATE VIEW HumanResources.EmployeeListASSELECT BusinessEntityID, JobTitle, HireDate,VacationHoursFROM HumanResources.Employee;

SELECT * FROM HumanResources.EmployeeList

CREATE FUNCTION Sales.fn_LineTotal (@SalesOrderID INT)RETURNS TABLEASRETURN

SELECT SalesOrderID,CAST((OrderQty * UnitPrice * (1 - SpecialOfferID))AS DECIMAL(8, 2)) AS LineTotalFROM Sales.SalesOrderDetailWHERE SalesOrderID = @SalesOrderID ;

Writing queries with derived tables

SELECT FROM (

) AS ;

Derived Tables Must

Have an alias Have names for all columns

Have unique names for all columns

Not use an ORDER BY clause (without TOP or OFFSET/FETCH)

Not be referred to multiple times in the same query

Derived Tables May

Use internal or external aliases for columns

Refer to parameters and/or variables

Be nested within other derived tables

DECLARE @emp_id INT = 9;SELECT orderyear, COUNT(DISTINCT custid) AS cust_countFROM (

SELECT YEAR(orderdate) AS orderyear, custidFROM Sales.OrdersWHERE empid=@emp_id

) AS derived_yearGROUP BY orderyear;

WITH CTE_year AS(SELECT YEAR(OrderDate) AS OrderYear, customerIDFROM Sales.SalesOrderHeader)SELECT orderyear, COUNT(DISTINCT CustomerID) AS CustCountFROM CTE_yearGROUP BY OrderYear;

STDEV STDEVP VAR VARP

SUM MIN MAX AVG COUNT COUNT_BIG

CHECKSUM_AGG GROUPING GROUPING_ID

Common Statistical Other

Views are named tables expressions with definitions stored in a database

that can be referenced in a SELECT statement just like a table

Views are defined with a single SELECT statement and then saved in the

database as queries

Table-valued functions are created with the CREATE FUNCTION. They

contain a RETURN type of table

Derived tables allow you to write more modular queries

as named query expressions that are created within an outer SELECT

statement. They represent a virtual relational table so are not stored in

the database

CTEs are similar to derived tables in scope and naming requirements but

unlike derived tables, CTEs support multiple definitions, multiple

references, and recursion

Querying Microsoft SQL Server 2012 Jump Start

01 | Introducing SQL Server 2012

SQL Server types of statements; other SQL statement elements; basic SELECT statements

02 | Advanced SELECT StatementsDISTINCT, Aliases, scalar functions and CASE, using JOIN and MERGE; Filtering and sorting data, NULL

values

03 | SQL Server Data Types Introduce data types, data type usage, converting data types, understanding SQL Server function types

04 | Grouping and Aggregating dataAggregate functions, GROUP BY and HAVING clauses, subqueries; self-contained, correlated, and EXISTS; Views, inline-table

valued functions, and derived tables

| Lunch BreakEat, drink, and recharge for the afternoon session

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