Sql xp 02

Retrieving Result Sets

Objectives
In this lesson, you will learn to:
Use wildcards
Use the IS NULL and IS NOT NULL keywords
Use the ORDER BY clause
Use the TOP keyword
Use the DISTINCT keyword
Use aggregate functions in queries
Group result sets
Use the COMPUTE and COMPUTE BY clause

©NIIT SQL/lesson 2/Slide 1 of 52


2.D.1 Retrieving Rows Based on Pattern Matching
Jackson Demello of the Texas Times newspaper, is to be
contacted. However, there are three newspapers that contain
the words “Texas Times” along with other words. To ensure
that the right newspaper is contacted, details like the names
of the newspapers, the contact persons, and the telephone
numbers of the newspapers, which have “Texas Times” in
their names need to be displayed.



Task List
Create a format for query output
Draft the query
Execute the query
Verify that the query output is as per the required results



Create a format for the query output
Result:
The required output from the report is the name of the
newspaper, contact person, and the telephone numbers
The column headings required in the report are
cNewspaperName, vContactPerson and cPhone
The newspaper name should have the phrase “Texas
Times” in it
The format of the report is shown below:
cNewspaperName vContactPerson cPhone



Draft the query
String Operator
You can use the LIKE keyword to search for a string with
the wildcard mechanism
The LIKE keyword is used to select those rows that
match the specified portion of character string
Result:
The required information is available in the Newspaper
table
Since the newspaper name must have “Texas Times”,
and it could be prefixed or suffixed by anything, the wild
card to be used is %



Draft the query (Contd.)
Therefore, the query using the SELECT statement
should be:
SELECT cNewspaperName, vContactPerson,
cPhone
FROM Newspaper
WHERE cNewspaperName
LIKE '%Texas Times%'



Execute the query
Action:
In the Query Analyzer window, type the query
Execute the query



Verify that the query output is as per the required
results
Check whether:
The required columns are displayed
All the rows that meet the condition specified in the
WHERE clause are displayed



Just a Minute…
Write a query to display the details of all the contract
recruiters whose names begin with “J”.



2.D.2 Displaying Rows With Missing Values
The list of candidates for whom interviews are not yet
scheduled is required.

©NIIT SQL/lesson 2/Slide 10 of


Task List
Draft the query
Execute the query



Result:
The output requirement for the report is the names of the
candidates whose interview has not yet been scheduled



Draft the query
The IS NULL and IS NOT NULL Keywords
NULL is an unknown value or a value for which data is
not available
Syntax
SELECT column_list FROM table_name
WHERE column_name unknown_value_operator
Result:
The information is available in the ExternalCandidate
table
The condition is that the test date should be NULL


Draft the query
Therefore, the query using the SELECT statement should
be:
SELECT vFirstName, vLastName, dInterviewDate
FROM ExternalCandidate
WHERE dInterviewDate IS NULL



Execute the query
Action:
Execute the query



results
Check whether:
All rows that have a NULL value in the dInterviewDate
attribute are displayed



2.D.3 Displaying Data in a Specific Order
A report of all roles is required as inputs for further reviewing
of the number of vacancies. A report in the ascending order of
the position description is to be generated.



Task List
Draft the query
Execute the query



Result:
The output required in the report is the position code and
a description of the position available
The format of the report is given below:
cPositionCode cDescription



Result:
® The information is available in the Position table
® Therefore, the query using the SELECT statement
should be:
SELECT cPositionCode, vDescription
FROM Position
ORDER BY vDescription ASC



Execute the query
Action:
Execute the query



results
Check whether:
All rows are displayed by vDescription in ascending order



2.D.4 Displaying the Top Few Rows
Based on test scores, the top 3 external candidates have to
be short-listed for an interview. The tests were taken in
March 2001. All details of these candidates are required.



Task List
Draft the query
Execute the query



Result:
The output required from the query is details of the top 3
candidates
The column headings required by the report are the
attribute names of the table ExternalCandidate



Draft the query
The TOP Keyword
The TOP clause limits the number of rows returned in the
result set
Syntax
SELECT [TOP n [PERCENT]] column_name
[,column_name…]
FROM table_name
WHERE search_conditions
[ORDER BY [column_name[,column_name…]



Result:
The information required is available in the
ExternalCandidate table
All the external candidate details are required
be:
SELECT TOP 3 *
FROM ExternalCandidate
WHERE dTestDate = '3/1/01'
AND dTestDate = '3/31/01'
ORDER BY siTestScore DESC


Execute the query
Action:
In the Query Analyzer window, type:
Execute the query



results
Check whether:
The query output is as per the required result
The rows are in descending order of the test scores



The Distinct Keyword
The DISTINCT keyword removes duplicate rows from the
result set
Syntax
SELECT [ALL|DISTINCT] column_names
FROM table_name WHERE search_condition



Just a Minute…
Write a query that displays a list of cities from where
applications of external candidates have been received.



2.D.5 Displaying Aggregate Functions
The total number of newspapers in which advertisements for
recruitments are published is required.



Task List
Draft the query
Execute the query



Result:
The output requirement in the report is to display the total
number of newspapers in which advertisements for
recruitments are published
The heading to be used is “No. of Newspapers”
The format of the output is shown below:

No. of Newspapers



Draft the query
Aggregate Functions
Summarize the values for a column or a group of columns
within a table for which they are applied, and produce a
single value
Result:
The information is available in the Newspaper table
The aggregate function to be used is COUNT
be:
SELECT 'No.Of Newspapers’ =
COUNT(cNewspaperCode)
FROM Newspaper


Execute the query
Action:
In the Query Analyzer window, type:
Execute the query



results
Check whether the correct count of newspapers is displayed



Grouping Result Sets
The following clauses are used to group result sets:
GROUP BY: Summarizes the result set into groups
defined in the query using aggregate functions
GROUP BY ALL: The ALL keyword of the GROUP BY
clause is used to display all groups, including those
excluded from the WHERE clause
COMPUTE and COMPUTE BY: The COMPUTE clause
with the SELECT statement is used to generate summary
rows using the aggregate functions in the query results.
The COMPUTE BY clause further summarizes the result
set by columns



2.D.6 Generating a Summary Report
The effectiveness of advertisements for recruitments placed
in various newspapers needs to be analyzed. As a first step,
the number of advertisements placed in each newspaper is
required in the following format:

Newspaper Code No. Of Advts. Placed



Task List
Draft the query
Execute the query



Draft the query
The GROUP BY Clause
Syntax
SELECT column_list
FROM table_name
WHERE condition
GROUP BY [ALL] expression [, expression]
[HAVING search_condition]



The HAVING keyword in the SELECT query can be used to
select rows from the intermediate result set
Result:
The information is available in the NewsAd table
The number of advertisements placed in each newspaper is
required
The output needs to be grouped newspaper wise, so the
GROUP BY clause has to be used



be:
SELECT 'Newspaper Code' = cNewspaperCode,
'No. Of Advts. Placed'
= COUNT(cNewspaperCode)
FROM NewsAd
GROUP BY cNewspaperCode



Execute the query
Action
Execute the query



Verify that the query output is as per the planned
format
Check whether:
The number of advertisements published in each
newspaper is correct



GROUP BY ALL
The ALL keyword of the GROUP BY clause is used to display
all groups, including those excluded from the WHERE clause
Example
SELECT Type, Advance = SUM (Advance)
FROM Titles
WHERE Type IN ('business', 'mod_cook',
'trad_cook')
GROUP BY ALL Type



COMPUTE and COMPUTE BY
The COMPUTE clause with the SELECT statement is used
to generate summary rows using aggregate functions in the
query results
The COMPUTE BY clause can be used to calculate
summary values of the result set on a group of data
Syntax
SELECT column_list FROM table_name
ORDER BY column_name
COMPUTE aggregate_function (column_name) [,
aggregate_function (column_name)...]
[BY column_name [, column_name]...]



Just a Minute…
A list of external candidates who took a test, along with their
test scores, is required. The average of the test scores
needs to be printed at the bottom of the list.



Summary
In this lesson, you learned that:
SQL Server provides a pattern-matching method for string
expressions by using the LIKE keyword with the wildcard
mechanism
The LIKE keyword is used to select those rows that match
the specified portion of character string
In SQL Server terms, NULL is an unknown value or a value
for which data is not available
The NULL values can be retrieved from the table using the
IS NULL keyword in the WHERE clause



Summary (Contd.)
The DISTINCT keyword in the SELECT statement is used to
eliminate duplicate rows
The TOP clause limits the number of rows returned in the
result set
The GROUP BY clause organizes the summarized result set
into groups defined in a table with the help of the aggregate
functions
The HAVING clause restricts the result set to produce the
data based on a condition



Summary (Contd.)
The ALL keyword of the GROUP BY clause is used to
display all groups, including those excluded from the
WHERE clause
SQL Server provides the COMPUTE clause with the
SELECT statement to produce summary rows using
aggregate functions in the query results
The COMPUTE BY clause can be used to calculate
summary values of the result set on a group of data


Sql xp 02

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