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Module 4: Grouping andSummarizing Data

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Overview

Listing the TOP n Values

Using Aggregate Functions

GROUP BY Fundamentals

Generating Aggregate Values WithinResult Sets

Using the COMPUTE and COMPUTE BYClauses

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Listing the TOP n Values

Lists Only the First n Rows of a ResultSet

Specifies the Range of Values in theORDER BY Clause

Returns Ties if WITH TIES Is Used

USE northwind

SELECT TOP 5 orderid, productid, quantity

FROM [order details]

ORDER BY quantity DESC

GO

USE northwind

SELECT TOP 5 WITH TIES orderid, productid, quantity

FROM [order details]

ORDER BY quantity DESC

GO

Example 1

Example 2

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Using Aggregate Functions

Aggregate functionAggregate function DescriptionDescription

AVG Average of values in a numeric expression

COUNT Number of values in an expression

COUNT (*) Number of selected rows

MAX Highest value in the expression

MIN Lowest value in the expression

SUM Total values in a numeric expression

STDEV Statistical deviation of all values

STDEVP Statistical deviation for the population

VAR Statistical variance of all values

VARP Statistical variance of all values for the population

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Using Aggregate Functions with NullValues

Most Aggregate Functions Ignore NullValues

COUNT(*) Function Counts Rows with

Null Values

USE northwind

SELECT COUNT (*)

FROM employees

GO

USE northwind

SELECT COUNT(reportsto)

FROM employees

GO

Example 1

Example 2

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GROUP BY Fundamentals

Using the GROUP BY Clause

Using the GROUP BY Clause with theHAVING Clause

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Using the GROUP BY Clause

USE northwind

SELECT productid, orderid

,quantityFROM orderhist

GO

USE northwind

SELECT productid

,SUM(quantity) AS total_quantity

FROM orderhist

GROUP BY productid

GO

productidproductid total_quantitytotal_quantity

1 15

2 35

3 45

productidproductid orderidorderid quantityquantity

1 1 5

1 1 10

2 1 10

2 2 25

3 1 15

3 2 30

productidproductid total_quantitytotal_quantity

2 35

Only rows thatsatisfy theWHERE clauseare grouped

USE northwind

SELECT productid

,SUM(quantity) AS total_quantity

FROM orderhist

WHERE productid = 2

GROUP BY productid

GO

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Using the GROUP BY Clause with theHAVING Clause

USE northwind

SELECT productid, orderid

,quantity

FROM orderhist

GO

USE northwind

SELECT productid, SUM(quantity)

AS total_quantity

FROM orderhist

GROUP BY productid

HAVING SUM(quantity)>=30

GO

productidproductid total_quantitytotal_quantity

2 35

3 45

productidproductid orderidorderid quantityquantity1 1 5

1 1 10

2 1 10

2 2 25

3 1 15

3 2 30

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Generating Aggregate ValuesWithin Result Sets

Using the GROUP BY Clause with theROLLUP Operator

Using the GROUP BY Clause with the

CUBE Operator

Using the GROUPING Function

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Description

Using the GROUP BY Clause with theROLLUP OperatorUSE northwindSELECT productid, orderid, SUM(quantity) AS total_quantityFROM orderhist

GROUP BY productid, orderidWITH ROLLUPORDER BY productid, orderidGO

productidproductid orderidorderid total_quantitytotal_quantity

NULL NULL 95

1 NULL 15

1 1 5

1 2 10

2 NULL 35

2 1 102 2 25

3 NULL 45

3 1 15

3 2 30

Grand total

Summarizes only rows for productid 1

Detail value for productid 1, orderid 1

Detail value for productid 1, orderid 2

Summarizes only rows for productid 2

Detail value for productid 2, orderid 1

Summarizes only rows for productid 3

Detail value for productid 3, orderid 1

Detail value for productid 3, orderid 2

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1 represents summary valuesin the preceding column

0 represents detail values inthe preceding column

95

30

65

15

5

10

3510

25

45

15

30

Using the GROUPING FunctionSELECT productid, GROUPING (productid)

,orderid, GROUPING (orderid)

,SUM(quantity) AS total_quantity

FROM orderhist

GROUP BY productid, orderid

WITH CUBE

ORDER BY productid, orderid

GOproductidproductid

NULL

NULL

NULL

1

1

1

22

2

3

3

3

1

1

1

0

0

0

00

0

0

0

0

orderidorderid

NULL

1

2

NULL

1

2

NULL1

2

NULL

1

2

1

0

0

1

0

0

10

0

1

0

0

total_quantitytotal_quantity

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Avoid Using the COMPUTE or COMPUTE BY Clause

Index Frequently Aggregated Columns

Avoid Using Aggregate Functions with Null Values

Use the ORDER BY Clause to Guarantee a Sort Orde

Use the ROLLUP Operator Instead of the CUBE Operat

Recommended Practices

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Lab A: Grouping and SummarizingData

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Review

Listing the TOP n Values

Using Aggregate Functions

GROUP BY Fundamentals

Generating Aggregate Values WithinResult Sets

Using the COMPUTE and COMPUTE BYClauses