Download Joins and subqueries

Using Subqueries and Managing Databases
Objectives
In this lesson, you will learn to:
Use subqueries
Use subqueries with the IN clause
Use subqueries with the EXISTS clause
Use nested subqueries
Use correlated subqueries
Use the SELECT INTO statement
Use the UNION operator
View, rename, and delete databases
SQL/Lesson 4/Slide 1 of 45
Using Subqueries and Managing Databases
Subqueries
A subquery can be defined as a SELECT query that returns
a single value
Subqueries are nested within a SELECT, INSERT, UPDATE,
or DELETE statement
Subqueries can be used to retrieve data from multiple tables
and can be used as an alternative to a join
Subqueries can also be used inside the WHERE or HAVING
clause of the SELECT, INSERT, UPDATE, and DELETE
statements
SQL/Lesson 4/Slide 2 of 45
Using Subqueries and Managing Databases
4.D.1 Using one Query in Another
List the contract recruiters who live in the same city as the
external candidate Barbara Johnson.
SQL/Lesson 4/Slide 3 of 45
Using Subqueries and Managing Databases
Task List
Create a format for the query output
Identify the components of the query
Execute the query
Verify that the query output is as per the required results
SQL/Lesson 4/Slide 4 of 45
Using Subqueries and Managing Databases
Create a format for the query output
Result
 The required output from the query is the names of the
contract recruiters who reside in the same city as
'Barbara Johnson'
 The required data is present in the ContractRecruiter and
ExternalCandidate tables
SQL/Lesson 4/Slide 5 of 45
Using Subqueries and Managing Databases
Draft the query
Result
 The required information is available in the
ExternalCandidate and ContractRecruiter tables
 Therefore, the query using the SELECT statement should
be:
SELECT cName
FROM ContractRecruiter
WHERE cCity = (SELECT cCity
FROM ExternalCandidate
WHERE vFirstName = 'Barbara'
AND vLastName = 'Johnson')
SQL/Lesson 4/Slide 6 of 45
Using Subqueries and Managing Databases
Execute the query
Action:
 In the Query Analyzer window, type the query
 Execute the query
SQL/Lesson 4/Slide 7 of 45
Using Subqueries and Managing Databases
Verify that the query output is as per the required
results
 Action:
 Check whether:

The required rows are displayed
SQL/Lesson 4/Slide 8 of 45
Using Subqueries and Managing Databases
More on Subqueries
Subqueries with IN
 A subquery introduced with IN returns zero or more
values
 Example
SELECT Au_Id
FROM TitleAuthor
WHERE Title_Id IN
(SELECT Title_Id FROM Sales)
SQL/Lesson 4/Slide 9 of 45
Using Subqueries and Managing Databases
More on Subqueries (Contd.)
Subqueries with EXISTS
 A subquery, when used with the EXISTS clause, always
returns data in terms of a TRUE or FALSE value
 Example
SELECT Pub_Name
FROM Publishers
WHERE EXISTS (SELECT * FROM Titles
WHERE Type = 'business')
SQL/Lesson 4/Slide 10 of 45
Using Subqueries and Managing Databases
More on Subqueries (Contd.)
Subqueries with Aggregate Functions
 Aggregate functions can also be used in subqueries
 Example
SELECT
Title
FROM Titles
WHERE Advance > (SELECT AVG(Advance)
FROM Titles
WHERE Type = 'business')
SQL/Lesson 4/Slide 11 of 45
Using Subqueries and Managing Databases
More on Subqueries (Contd.)
Subqueries Restrictions
 SQL Server restricts the use of certain methods and
techniques, and forces the implementation of certain
standards while using subqueries. The restrictions
imposed are:

The column list of the SELECT statement of a
subquery introduced with a comparison operator can
include only one column

The column used in the WHERE clause of the outer
query should be compatible with the column used in
the SELECT list of the inner query
SQL/Lesson 4/Slide 12 of 45
Using Subqueries and Managing Databases
More on Subqueries (Contd.)

The ORDER BY clause and the GROUP BY clause
cannot be used in the inner query when =, !=, <, <=, >,
or >= are used in the main query, as the inner query
may return more than one value that cannot be
handled by the outer query
SQL/Lesson 4/Slide 13 of 45
Using Subqueries and Managing Databases
More on Subqueries (Contd.)
Nested Subqueries
 A subquery can itself contain one or more subqueries
 Example
SELECT 'Author Name' = SUBSTRING
(Au_Fname, 1, 1) + '. '+ Au_Lname
FROM Authors
WHERE Au_Id IN (SELECT Au_Id
FROM TitleAuthor
WHERE Title_Id =(SELECT
Title_Id FROM Titles
WHERE Title = 'Net Etiquette'))
SQL/Lesson 4/Slide 14 of 45
Using Subqueries and Managing Databases
More on Subqueries (Contd.)
Correlated Subqueries
 Can be defined as queries that depend on the outer
query for its evaluation
 Example
SELECT Title, Type, Advance
FROM Titles t1
WHERE t1.Advance > (SELECT AVG(t2.Advance)
FROM Titles t2 WHERE
t1.Type = t2.Type)
SQL/Lesson 4/Slide 15 of 45
Using Subqueries and Managing Databases
More on Subqueries (Contd.)
Queries With Modified Comparison Operators
 SQL Server provides the ALL and ANY keywords that can
be used to modify the existing comparison operator
SQL/Lesson 4/Slide 16 of 45
Using Subqueries and Managing Databases
4.D.2 Extracting Data Into Another Table
To carry out an analysis of the profile of candidates who have
applied for recruitment in May 2001, you need to copy their
details into a new table.
SQL/Lesson 4/Slide 17 of 45
Using Subqueries and Managing Databases
Task List
Identify the output requirements of the query
Draft the query
Execute the query
Verify that the query output is as per the required results
SQL/Lesson 4/Slide 18 of 45
Using Subqueries and Managing Databases
Identify the output requirements of the query
Result:
 The required output from the query is the transfer of data
from the ExternalCandidate table to a temporary table
called tempExternalCandidate
SQL/Lesson 4/Slide 19 of 45
Using Subqueries and Managing Databases
Draft the query
SELECT INTO Statement
 A SELECT statement with the INTO clause is used to
store the result set in a new table without a data definition
process. The SELECT INTO statement creates a new
table.
 Syntax
SELECT columns_list
INTO new_table_name
FROM table_name1, table_name2,………,
table_name n
WHERE condition1, condition2,……….,
condition n
SQL/Lesson 4/Slide 20 of 45
Using Subqueries and Managing Databases
Draft the query (Contd.)
 Example
SELECT Title_Id, Title
INTO NewTitles
FROM Titles
WHERE Price > $15
Result:
 The required information is available in the
ExternalCandidate table
 Therefore, the query using the SELECT statement should
be:
SQL/Lesson 4/Slide 21 of 45
Using Subqueries and Managing Databases
Draft the query (Contd.)
SELECT * INTO tempExternalCandidate
FROM ExternalCandidate
WHERE DATEPART(mm,dDateOfApplication)= 5
AND DATEPART(yyyy,dDateOfApplication)= 2001
SQL/Lesson 4/Slide 22 of 45
Using Subqueries and Managing Databases
Execute the query
Action
 In the Query Analyzer window, type the query
 Execute the query
SQL/Lesson 4/Slide 23 of 45
Using Subqueries and Managing Databases
Verify that the query output is as per the required
results
 Action:
Check whether:
The
target table has all data from the source table
Just a Minute…
Write a query to copy all the contents of InternalCandidate to
a table called backupInternalCandidate.
SQL/Lesson 4/Slide 24 of 45
Using Subqueries and Managing Databases
4.D.3 Combining Data From Two Tables
A list of contract recruiters and recruitment agencies along
with their phone numbers is required.
SQL/Lesson 4/Slide 25 of 45
Using Subqueries and Managing Databases
Task List
Create a format for the query output
Draft the query
Execute the query
Verify that the query output is as per the required results
SQL/Lesson 4/Slide 26 of 45
Using Subqueries and Managing Databases
Create a format for the query output
Result:
 The required output from the query is a single list of
names and phone numbers of contract recruiters and
recruitment agencies
SQL/Lesson 4/Slide 27 of 45
Using Subqueries and Managing Databases
Draft the query
UNION Operator
 Is used to combine the result set of two or more queries
 Syntax
SELECT column_list [INTO new_table_name]
[FROM clause] [WHERE clause]
[GROUP BY clause][HAVING clause]
[UNION [ALL]
SELECT column_list
[FROM clause] [WHERE clause]
[GROUP BY clause][HAVING clause]...]
[ORDER BY clause]
[COMPUTE clause]
SQL/Lesson 4/Slide 28 of 45
Using Subqueries and Managing Databases
Draft the query (Contd.)
Result
 The required information is available in the
ContractRecruiter and RecruitmentAgencies tables
 Therefore, the query using the SELECT statement should
be:
SELECT cName,cPhone
FROM ContractRecruiter
UNION
SELECT cName, cPhone
FROM RecruitmentAgencies
SQL/Lesson 4/Slide 29 of 45
Using Subqueries and Managing Databases
Execute the query
Action
 In the Query Analyzer window, type the query
 Execute the query
SQL/Lesson 4/Slide 30 of 45
Using Subqueries and Managing Databases
Verify that the query output is as per the required
results
 Action:
 Check whether:

All the required columns are displayed

All rows from both tables are displayed as one list
Just a Minute…
Display the list of college names, newspaper names, and
their addresses in the following format:
Name
Address
SQL/Lesson 4/Slide 31 of 45
Using Subqueries and Managing Databases
Databases
A database is a collection of tables and objects such as
views, indexes, stored procedures, and triggers
System Databases
 master Database-records all the server-specific
configuration information, including authorized users,
databases, system configuration settings, and remote
servers
 tempdb Database-is a temporary database that is used
as an interim storage area
 model Database-acts as a template or a prototype for the
new databases
 msdb Database-supports SQL Server Agent
SQL/Lesson 4/Slide 32 of 45
Using Subqueries and Managing Databases
Databases (Contd.)
System Tables
 Are a set of tables that are used by SQL server to store
information about configuration, security, and object
information
 SQL Server manages each database with the help of the
system tables, which contain all the system information
Just a Minute…
What is the purpose of model database in SQL Server?
SQL/Lesson 4/Slide 33 of 45
Using Subqueries and Managing Databases
Databases (Contd.)
Files: The three types of files that a database has are:

Primary

Secondary

Transaction Log
Filegroup: Is a collection of files
A file or filegroup cannot be used by more than one
database
A file can be a member of only one filegroup
SQL/Lesson 4/Slide 34 of 45
Using Subqueries and Managing Databases
Viewing a Database
The information regarding the database such as owner, size,
date of creation, and status can be viewed using the
following:
sp_helpdb database_name
SQL/Lesson 4/Slide 35 of 45
Using Subqueries and Managing Databases
Renaming a Database
The name of a database can be changed using the
sp_renamedb command. The database should not be in use
when it is being renamed, and it should be set to the singleuser mode
 Syntax
sp_renamedb 'old_name', 'new_name'
SQL/Lesson 4/Slide 36 of 45
Using Subqueries and Managing Databases
Deleting a Database
The DROP DATABASE statement is used to delete a
database
 Syntax
DROP DATABASE database_name
Just a Minute…
List the three types of operating system files that store the
data and objects of SQL Server database.
SQL/Lesson 4/Slide 37 of 45
Using Subqueries and Managing Databases
Summary
In this lesson, you learned that:
Subqueries are nested within a SELECT, INSERT, UPDATE,
or DELETE statement
A subquery can be used inside the WHERE or HAVING
clauses of the outer SELECT, INSERT, UPDATE, or DELETE
statements
The subquery introduced with IN or NOT IN returns zero or
more values
The subquery used with the EXISTS clause returns data in
terms of TRUE or FALSE
SQL/Lesson 4/Slide 38 of 45
Using Subqueries and Managing Databases
Summary (Contd.)
A subquery can contain one or more subqueries. There is no
restriction on the number of subqueries one can include with
the SELECT, INSERT, UPDATE, or DELETE statements
A correlated subquery can be defined as a query that depends
on the outer query for its evaluation
A SELECT statement with an INTO clause can be used to
store the result set in a new table without any data definition
process
The UNION operator is used to combine the result set of two
or more queries into one
SQL/Lesson 4/Slide 39 of 45
Using Subqueries and Managing Databases
Summary (Contd.)
By default the result set of a UNION operator removes the
duplicate rows from the queries combined, unless an ALL
clause is specified with the UNION operator
A database consists of a collection of tables with data and
other objects such as views, indexes, stored procedures, and
triggers
SQL Server has the following system databases:
 master
 tempdb
 model
 msdb
SQL/Lesson 4/Slide 40 of 45
Using Subqueries and Managing Databases
Summary (Contd.)
SQL Server stores its configuration, security, and object
information in tables called system tables
A database consists of the following types of files:
 Primary data file
 Secondary data file
 Transaction log file
A filegroup is a collection of files. Filegroups allow files to be
grouped together
A database comprises of a primary filegroup and any userdefined filegroup(s)
SQL/Lesson 4/Slide 41 of 45
Using Subqueries and Managing Databases
Summary (Contd.)
Creation of a database involves determining the name of the
database, the size of the database, and the files used to store
data in the database
sp_helpdb is used to view the information regarding a
database
sp_renamedb is used to rename a database
The DROP DATABASE statement is used to delete a database
SQL/Lesson 4/Slide 42 of 45