SQL/lesson 2/Slide 1 of 45 Retrieving Result Sets Objectives In this lesson, you will learn to: * Use wildcards * Use the IS NULL and IS NOT NULL keywords

SQL/lesson 2/Slide 1 of 45

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



Retrieving Rows Based on Pattern Matching

A author Sheryl, staying at Blonde street is to be contacted. However, there are many address that contain the word “Blonde” along with other words. To ensure that the right person is contacted, details like the names of the person, the address, and the telephone numbers of the author, which have “Blonde” in their address 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



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 Authors table

Since the address must have “Blonde”, 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 * from authors where address like '%Blonde%'



Execute the query

Action:

In the Query Analyzer window, type the query

Execute the query




Check whether:

The required columns are displayed

All the rows that meet the condition specified in the WHERE clause are displayed



Wait a while…

Write a query to display the details of all the Jobsjob description begin with “M”.

Use Jobs Table of pubs.



Displaying Rows With Missing Values

The list of books for whom royalty is not yet decided is required.



Task List

Create a format for the query output

Draft the query

Execute the query




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 Titles table of pubs

The condition is that the royalty should be NULL



Draft the query


SELECT * FROM titles WHERE royalty IS NULL




Check whether:

The required columns are displayed

All rows that have a NULL value in the Royalty attribute are displayed



Wait a while…

A list of publishers is required where state information must be available. Use publishers table of pubs



Displaying Data in a Specific Order

A report of all employee is required as inputs for further reviewing. A report in the ascending order of the FirstName is to be generated.



Task List


Draft the query

Execute the query




Draft the query

The ORDER BY Clause

Syntax

SELECT select_list FROM table_name [ORDER BY column_name

[ASC|DESC ] ]



Draft the query (Contd.) Result:

The information is available in the Employee table Therefore, the query using the SELECT statement

should be:

SELECT * FROM employee ORDER BY fname



Displaying the Top Few Rows

Based on price, the top 3 Book details have to be displayed.



Task List


Draft the query

Execute the query





Result:

The output required from the query is details of the top 3 costlier Books.

The column headings required by the report are the attribute names of the table Titles.



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:


SELECT TOP 3 * FROM titles ORDER BY Price DESC



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



Wait a while…

Write a query that displays a list of states from where publishers are staying.

Use publishers table.



Displaying Aggregate Functions

The total number of authors who are having contract value as 1 is required.



Task List


Draft the query

Execute the query




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 Authors table

The aggregate function to be used is COUNT


select count(*) from authors where contract = 1



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



Generating a Summary Report

The information of employees is required in the following format:

Job ID No. Of Employees



Task List

Draft the query

Execute the query




Draft the query

The GROUP BY Clause

SyntaxSELECT column_listFROM table_nameWHERE condition GROUP BY expression [,

expression][HAVING search_condition]




Result:

The information is available in the Employee table

The output needs to be grouped Job_ID wise, so the GROUP BY clause has to be used





SELECT job_id, 'Total Count'=COUNT(emp_id) FROM employee Group BY job_id



WHERE CLAUSE IN GROUP BY

Example

SELECT job_id, 'Total Count'=COUNT(emp_id) FROM employee WHERE job_lvl IN (100,200) Group BY job_id



The HAVING keyword in the SELECT query can be used to select rows from the intermediate result set

SELECT job_id, 'Total Count'=COUNT(emp_id) FROM employee Group BY job_id HAVING COUNT(job_id) >= 4



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]...]



A list of all the books from the titles table is to be displayed along with the sum of advance.

The COMPUTE clause with the SELECT statement will have to be used.



The query can be written as:

select * from Titles compute sum(advance)



A list of all the books from the titles table is to be displayed along with the sum of advance for each publisher id. The COMPUTE BY clause can be used to calculate

summary values of the result set on a group of data



The query can be written as:

SELECT * FROM Titles ORDER BY pub_id COMPUTE SUM(advance)BY pub_id



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

Documents

SQL/lesson 2/Slide 1 of 45 Retrieving Result Sets Objectives In this lesson, you will learn to: * Use wildcards * Use the IS NULL and IS NOT NULL keywords