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ITBIS373 Database
Development
Lecture3c - Chapter 3:
Using SQL Queries to
Insert, Update, Delete, and
View Data
Guide to Oracle 10g
Lesson C Objectives
After completing this lesson, you should be
able to:
 Create SQL queries that join multiple tables
 Create nested SQL queries
 Combine query results using set operators
 Create and use database views
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Joining Multiple Tables

Join


Combine data from multiple database tables using
foreign key references
Syntax
SELECT column1, column2, …
FROM table1, table2
WHERE table1.joincolumn =
table2.joincolumn
AND search_condition(s);
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Joining Multiple Tables
(continued)

Must qualify column name in SELECT clause


Join condition


Specify name of table that contains column
followed by period then column name
Specifies table names to be joined and column
names on which to join tables
SQL supports multiple types of join queries
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Inner Joins



Simplest type of join
VALUES in one table equal to values in other
table
Also called:




Equality join
Equijoin
Natural join
Query design diagram
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Fig 3-43 to retrieve the student Id, student last and
first names, advisor ID, and advisor last name.
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
In SQL queries, you can join any number of
tables in SELECT command. When join
tables, the name of each table in the query
must appear in the FROM clause. This
includes tables whose columns are display
columns, which are columns that appear in
the SELECT clause, and whose columns are
search columns, which appear in search
condition. The primary key and foreign key
columns on which you join the tables are
called join columns.
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

When you join multiple tables, sometimes
you must join the tables using an
intermediary table whose columns are not
display or search columns, but whose
columns are join columns that serve to join
the two tables.
For example, suppose you want to create a
query that lists the last names of all faculty
members who teach during the Summer
2007 term.
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Visual Representation of the
Northwoods University
Database
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A linking table does not contribute any as display columns
or search condition columns, but contains join columns that
link the other tables through shared foreign key values.
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




Some times queries that join multiple tables can
become complex. For example, suppose that you
want to create a query to display the COURSE_NO
and GRADE values for each of student ‘Tammy
Jones’ courses. This query requires you to join four
table:
STUDENT (to search for S_FIRST and S_LAST),
ENROLLMENT (to display GRADE),
COURSE to display COURSE_NO), and
COURSE_SECTION (to join ENROLLMENT to
COURSE using the C_SEC_ID join column).
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Deriving a SQL Query From a
Query Design Diagram
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
If you accidentally omit a join condition in a multipletable query, the output retrieves more rows than you
expect. When you omit a join condition, the query
creates a Cartesian product, whereby every row in
one table is joined with every row in the other table.
For example , suppose you repeat the query to
show each student row, along with each student’s
advisor (see Fig 3-43), but you omit the join
condition. Every row in the STUDENT table (six
rows) is joined with every row in the FACULTY table
(five rows). The result is 6 times 5 rows, or 30 rows.
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Outer Join



An inner join returns rows only if values exist in all
tables that are joined. If no values exist for a row in
one of the joined tables, the inner join does not
retrieve the row. For example suppose you want to
retrieve the different locations of the courses
included in the COURSE_SECTION table.
This query requires joining rows in the LOCATION
and COURSE_SECTION tables.
Not every location in the LOCATION table has an
associated COURSE_SECTION row, so the query
retrieves rows only for locations that have
associated COURSE_SECTION rows.
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SQL> SELECT c_sec_id, location.loc_id
2 From course_section, location
3 Where course_section.loc.id = location.loc_id;
C_SEC_ID
LOC_ID
----------------------1
1
11
1
3
2
8
3
6
5
7
5
10
5
13
5
9
5
4
6
12
6
5
6
2
7
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


An outer join returns all rows from one table
, which is called the inner table. An outer join
also retrieves matching rows from a second
table, which is called the outer table.
The query designer specifies which table is
the inner table and which table is the outer
table.
In this case, because you want to retrieve all
of the rows in the LOCATION table, you
specify LOCATION as the inner table.
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Outer Joins

Returns all rows from one table


And matching rows from second table


Called inner table
Called outer table
Syntax
inner_table.join_column =
outer_table.join_column(+)
The outer join operator (+) signals the DBMS to insert a NULL value
for the columns in the outer table that do not have matching rows
in the inner table.
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Self-Joins

Sometimes a relational database table contains a foreign key
that references a column in the same table. For example, at
Northwood's University each assistant and associate professor is
assigned to full professor who serves as the junior professor’s
supervisor.
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Self-Joins







To create a query that lists the names of each junior faculty
member and the names of their supervisor, you must join the
FACULTY table to itself.
When you create a query that joins a table to it self, you create a selfjoin.
To create a self-join, you must create a table alias and structure the
query as if you are joining the table to a copy of itself.
The syntax to create a table alias in the FORM clause is:
FROM table1 alias1,……
When you create a table alias, you must the use the table alias, rather
than the table name, to qualify column names in the SELECT clause
and in join condition.
T o make the process easier to understand, you create two table
aliases _FAC for faculty version of the table and SUPER for the
supervisor version of the same table, as shown in Fig 3-51.
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PARENT_PROJECT
P_ID
Self Joins
PROJECT_NAME
1 Hardware Support Intranet
CLIENT_ID
MGR_ID
PARENT_P_ID
2
105
2 Hardware Support Interface
2
103
1
3 Hardware Support Database
2
102
1
4 T eller Support System
4
105
5 Internet Advertising
6
105
6 Network Design
6
104
7 Exploration Database
5
102
5
SUB_PROJECT
P_ID
PROJECT_NAME
1 Hardware Support Intranet
CLIENT_ID
MGR_ID
PARENT_P_ID
2
105
2 Hardware Support Interface
2
103
1
3 Hardware Support Database
2
102
1
4 T eller Support System
4
105
5 Internet Advertising
6
105
6 Network Design
6
104
7 Exploration Database
5
102
5
PROJECT
P_ID
PROJECT_NAME
1 Hardware Support Intranet
CLIENT_ID
MGR_ID
PARENT_P_ID
2
105
2 Hardware Support Interface
2
103
1
3 Hardware Support Database
2
102
1
4 T eller Support System
4
105
5 Internet Advertising
6
105
6 Network Design
6
104
7 Exploration Database
5
102
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Self Join Example
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Creating Nested Queries

Nested query


Consists of main query and one or more
subqueries
Main query


First query that appears in SELECT command
Subquery

Retrieves values that main query’s search condition
must match
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Creating Nested Queries with
Subqueries that Return a
Single Value
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The query in Fig 3-54 to retrieve the names of all
students who have the same S_CLASS value as
student Jorge Perez.
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Creating Subqueries that
Return Multiple Values.

To create a nested query in which the
subquery retrieves multiple values. You must
use IN comparison operator instead of the
equal to comparison operator.
Ex: To retrieve the names of all students who have
enrolled in the same course sections as Jorge
Perez. Note that the main query’s search
conditions uses the IN comparison operator,
because the sub-query returns multiple values.
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ENROLLEMENT
S_ID
C_SEC_ID
PE100
1
PE100
5
PE100
6
PE100
9
JO100
1
JO100
6
JO100
9
MA100
1
JO101
5
JO101
9
GRADE
B
A
B
B
C
C
C
B
C
C
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Using Multiple Subqueries Within
a Nested Query

Use AND and OR operators


To join search conditions associated with
subqueries.
Ex: Fig 3-53 is used to retrieve the names of all
students who have the same S_CLASS value as
Jorge Perez and who have also been enrolled in
course section with him
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Creating Nested Subqueries

Nested subquery

Subquery that contains second subquery that
specifies its search expression
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USING SET Operator to Combine
Query Results

UNION set operator


Joins output of two unrelated queries into single output
result
Syntax
query1 UNION query2;
Both queries must have the



same number of display columns in their
SELECT clauses
must have the same data type
For example, if the display columns retuned by query1
are a NUMBER data column and then a VARCHAR2 data
column, then the display columns returned by query2
must also be a NUMBER data column followed by a
VARCHAR2 data column.

UNION ALL operator

Same as UNION but includes duplicate rows
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Ex: Create a telephone directory of every student
and faculty member at Northwood's University
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INTERSECT



Finds intersection in two queries
Requires that both queries have same
number and data types of display columns
in SELECT statement
Automatically suppresses duplicate rows.
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INTERSECT
Some queries require an output that finds the
intersection, or matching rows, in two unrelated queries.
For example, suppose you need to find a list of faculty
members whose offices are in the BUS building and who
have also taught a course in the BUS building.
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MINUS

To find difference between two unrelated
query result list.

As with the UNION and INTERSECT operators, the
MINUS operator requires that both queries have the
same number of display columns in the SELECT
statement, and that each column in the first query has
the same data type as corresponding column in the
second query.
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Creating and Using Database
Views

Source query



Used to create view
Specify subset of single table’s columns or rows
or join multiple tables
Updatable views

Can be used to update database
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Database Views




Logical table based on a query
Does not physically exist in the database
as table
Presents data in a different format from
underlying tables
Uses:


Security
Simplifying complex queries
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Database Views

Creating a view:
CREATE VIEW view_name AS
SQL_command;

Views can be queried just like tables:
SELECT *
FROM view_name;
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Simple Views


Based on SQL query that retrieves data from
only one table
View can support all table DML operations:




INSERT
UPDATE
DELETE
Can also execute update action queries and
delete action queries using view

Just as with database table
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Complex Views


Based on query that retrieves data from
multiple tables
Can only be used to support SELECT
operations

No DML operations supported
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Creating Views
If there is possibility that you have already created a
view using a specific name, you can use the
following command to create or replace the
existing view according to this syntax.
CREATE OR REPLACE VIEW view_name
AS source_query;
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Ex: This view contains all of the FACULTY columns
except F_PIN and F_IMAGE
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Executing Action Queries Using Views

1- To insert a row using the FACULTY_VIEW



INSERT INTO faculty_view VALUE (6,’may’,’Lisa,’I’,11,’7155552508’,’INST’)
2- Type SELECT * FROM faculty_view; to
determine whether the new faculty member is
included in the table.
Type DELETE FROM faculty_view WHERE f-last =‘MAY’;
to delete the new faculty member.
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Retrieving Rows from Views.


You can query a view using a SELECT
statement, just as with a database table, and
use the view in complex queries that involve
join operations and subqueries.
You create a query that joins
FACULTY_VIEW with the LOCATION to list
the names of each faculty member, along
with the building code and room number of
the faculty member’s office.
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Removing Views

DROP VIEW command


Remove view from user schema
Syntax


DROP VIEW view_name;
Ex: DROP VIEW faculty_view;
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Selecting Records For Update
 Syntax:
SELECT column1, column2, …
FROM table1, table2, …
WHERE search and join conditions
FOR UPDATE OF column1, column2, …
NOWAIT;
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
The NOWAIT command causes the system to generate an error
message immediately if another user has previously locked the
selected records. If the NOWAIT command is omitted, the
system forces the user to “wait” until the requested records are
unlocked, and the user can do no further processing.
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Dynamic SQL Queries


Queries that allow users to specify search
conditions at runtime
Approaches


Substitution Values
Runtime Variables
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Using Substitution Values


Created when search expression is prefaced
with an ampersand (&)
System then prompts user for value
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Using Runtime Variables

Runtime variable: variable defined in
SQL*Plus environment

Syntax:
DEFINE variable_name = variable_value;

You can then substitute the variable name
for a query search condition value
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Using Runtime Variables

Example:
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Indexes

Index: Separate table is
maintained that shows index
keys and physical locations
of corresponding records


In Oracle, ROWID is
translated to physical
location of row on disk
Improves response time of
searches and joins
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ROWID
Brown
13387289
Jones
13879872
Smith
58925789
Helgeson
29875018
68
Using Indexes
Create table index AFTER table is
populated with data
 Indexes make INSERT, UPDATE,
and DELETE operations slower
because index must also be
maintained

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Indexing Strategies

A table can have indexes on multiple fields



Create indexes based on fields used for search or
join operations
 Typically, indexes only speed retrievals when <15%
of the table records are involved
Each additional index adds processing
overhead for INSERT, UPDATE, and DELETE
operations
In Oracle, primary keys are automatically
indexed
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Creating Indexes
 Syntax:
CREATE INDEX index_name
ON tablename(index_field);
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Summary


INSERT action query
SQL search condition




UPDATE action query
DELETE command
SELECT query


Match one or more database rows
DISTINCT qualifier
Single row and group functions
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Summary (continued)


Can change appearance of SQL*Plus
environment
Join multiple tables in SELECT query





Inner join
Outer join
Nested queries
Set operators
Views
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