The document provides an overview of SQL queries focusing on inserting, updating, deleting, and viewing data, specifically through joining multiple tables. It explains different types of joins, including inner joins, outer joins, and self-joins, as well as how to create nested queries and use set operators to combine results. Additionally, it covers creating and managing database views and the syntax for each operation.

1. Using SQL Queries to Insert,
Update, Delete, and View Data:
Joining Multiple Tables
© Abdou Illia MIS 4200 - Spring 2015
Monday 2/9/2015

2. 2
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

3. 3
Joining Multiple Tables
a Join
– Combines data from multiple tables using foreign key
references
Syntax
SELECT column1, column2, …
FROM table1, table2
WHERE table1.joincolumn = table2.joincolumn
AND search_condition(s);
SELECT s_id, s_last, f_last
FROM student, faculty
WHERE student.f_id = faculty.f_id
AND f_last IN (‘Marx’, ‘Zhulin’);

4. 4
Joining Multiple Tables (continued)
Must qualify column name in SELECT clause
– Specify name of table that contains column followed
by period then column name
– Example: SELECT s_id, s_last, student.f_id
Join condition
– Specifies table names to be joined and column names
on which to join tables
– Example: WHERE student.f_id = faculty.f_id

5. 5
Inner Joins
Simplest type of join
Also called: Equality join, Equijoin, Natural join
VALUES in one table equal to values in other table
Query design diagram helps get the query right
SELECT s_id, s_last, s_first, student.f_id, f_last
FROM student, faculty
WHERE student.f_id = faculty.f_id;
Could be replaced by:
FROM Student NATURAL JOIN faculty;

6. 6
Display column, search column, join column
Display columns: appear in SELECT clause
Search columns: appear in search condition
Join columns: primary key and foreign key column
on which you join the tables.
Linkage table: contains join column to link other
tables through foreign key values.
SELECT f_last
FROM faculty, course_section, term
WHERE faculty.f_id = course_section.f_id
AND course_section.term_id = term.term_id
AND term_desc = 'Summer 2007';

7. 7
Deriving a SQL Query From a Query
Design Diagram
 4 tables, 3 links
 All 4 tables must be named in the
FROM clause
 Query must have 3 join conditions
because there are 3 links
 Always 1 fewer join condition than
number of tables that query joins.
 If you omit one join condition, the
query creates a Cartesian product
(every row in one table is joined with
every row in other table) with more
row than expected.
SELECT course_name, grade
FROM student, enrollment, course_section, course
WHERE student.s_id = enrollment.s_id
AND enrollment.c_sec_id = course_section.c_sec_id
AND course_section.course_no = course.course_no
AND s_last = 'Jones'
AND s_first = 'Tammy';
Search conditions

8. 8
Outer Joins
Inner joins return row only if values exist in all joined
tables
Outer joins return
all rows from one table (called inner table) and
only matching rows from second table (outer table)
Syntax: inner_table.join_col = outer_table.join_col(+)
(+) operator signals Oracle to insert NULL for columns from the outer table with no matching rows in the inner table.

9. 9
Self-join
Query that joins table to itself
Must create table alias
– Alternate name assigned to table in query’s FROM clause
– Syntax: FROM table1 alias1, table1 alias2 …

10. 10
Creating Nested Queries
 Nested query
– Consists of a 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
 Subquery is evaluated first. Then, DBMS substitute
subquery’s output into main query.

11. Creating Nested Queries
11
Q: What would happen if a subquery generated more
values than the main query is expecting?

12. 12
Creating subqueries that return multiple values

13. 13
Using Multiple Subqueries Within a
Nested Query
 Use AND and OR operators
– To join search conditions associated with subqueries

14. 14
Using SET operators to combine Query Results
 UNION
– Queries must have
same number of
display column in
their SELECT clause
– Corresponding display
columns must have
same data type
Note: S_LAST, S_FIRST, S_PHONE used as
display title even though there are faculty
members names displayed along with students.

15. 15
Using SET operators to combine Query Results
 INTERSECT
– Queries must have
same number of
display column in
their SELECT clause
– Corresponding display
columns must have
same data type
– Suppresses duplicates

16. 16
Using SET operators to combine Query Results
 MINUS
– Queries must have
same number of
display column in
their SELECT clause
– Corresponding display
columns must have
same data type
– Suppresses duplicates
– Finds difference
between two query
results

17. 17
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
 Syntax
CREATE VIEW view_name
AS source_query;
– Or
CREATE OR REPLACE VIEW view_name
AS source_query;

18. 18
Removing Views
DROP VIEW command
– Remove view from user schema
– Syntax
•DROP VIEW view_name;