1. Creating and Maintaining
Database Systems
Creating and Maintaining
Database Objects
Part 2
Teaching Tip: If you are using this slideshow in a computer classroom, students can enter commands to the MY_FACULTY and MY_STUDENTS tables as you introduce them. Before using this slideshow, create the tables using the following commands:
CREATE TABLE my_faculty
(f_id NUMBER(6),
f_name VARCHAR2(30));
CREATE TABLE my_students
(s_name VARCHAR2 (30), s_dob DATE, s_class CHAR(2), s_age NUMBER(2));
Then have students enter commands as they are introduced.

2. Date Arithmetic
To find a date that is a specific number of days before or after a known date, add or subtract the number from the known date
Example:
SELECT order_date + 30
FROM cust_order;

3. Date Arithmetic
To find the number of days between two known dates, subtract the later date from the earlier date
Example:
SELECT SYSDATE – s_dob
FROM my_students;

4. Date Functions ADD_MONTHS Example:
returns a date that is a specific number of months after a given date
Example:
SELECT ADD_MONTHS(SYSDATE, 6)
FROM dual;

5. Date Functions LAST_DATE Example:
Returns the date that is the last day of the month specified in the current date
Example:
SELECT LAST_DATE(order_date)
FROM cust_order
WHERE order_id = 1057;

6. Date Functions MONTHS_BETWEEN Example:
Returns the number of months between two input dates
Example:
SELECT MONTHS_BETWEEN(order_date, SYSDATE)
FROM cust_order
WHERE order_id = 1057;

7. Group Functions
Used to perform an operation on a field from a group of retrieved records
AVG (average of all retrieved values)
COUNT (number of records retrieved)
MAX (maximum value retrieved)
MIN (minimum value retrieved)
SUM (sum of all retrieved values)

8. Group Function Examples
SELECT AVG (s_age) FROM my_students;
SELECT MAX (s_age) FROM my_students;
SELECT MIN (s_age) FROM my_students;
SELECT SUM (s_age) FROM my_students;

9. Using the GROUP BY Clause
GROUP BY must be used if some columns in the SELECT clause are used in a group function and some are not
Group all fields that are not included in the group function
Example:
SELECT s_class, AVG(s_age)
FROM my_students
GROUP BY s_class;

10. Creating Alternate Column Headings in SQL*Plus
Syntax:
SELECT column1 “heading1”, column2 “heading2”, …
Example:
SELECT (SYSDATE – s_dob) “Student Age”
FROM my_students;

11. Creating a Column Alias
Column alias: alternate column name that can be referenced in the ORDER BY and GROUP BY clauses
Syntax:
SELECT column1 AS alias1 …
Example:
SELECT (SYSDATE – s_dob) AS age_alias
ORDER BY age_alias

12. Dynamic SQL Queries
Queries that allow users to specify search conditions at runtime
Approaches
Substitution Values
Runtime Variables

13. Using Substitution Values
Created when search expression is prefaced with an ampersand (&)
System then prompts user for value

14. 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

15. Using Runtime Variables
Example:

16. Formatting Data Using the TO_CHAR Function
Used to display NUMBER and DATE values using a specific format mask
Syntax:
TO_CHAR(fieldname, ‘format_mask’);

17. Join Queries
Retrieve data from multiple tables by joining tables using foreign key references
Join query types:
Inner (equality)
Outer
Self
Inequality

18. Inner Joins
One record is retrieved for each matching row

19. Inner Joins
Syntax:
SELECT column1, column2, …
FROM table1, table2
WHERE table1.join_column =
table2.join_column
You must include a join condition for every link between 2 tables
Join condition

20. Inner Joins
Example:
SELECT s_name, f_name
FROM student, faculty
WHERE student.f_id = faculty.f_id;
If you have N tables in the FROM clause, you must have (N - 1) join conditions

21. Qualifying Field Names
If a field in the SELECT clause exists in multiple tables in the FROM clause, you must qualify the field name by prefacing it with either table’s name

22. Process for Designing Complex Inner Join Queries
Identify all of the tables involved in the query, and label:
Display fields
Join fields
Search fields
Write the query
List all display fields in the SELECT clause
List all table names in the FROM clause
List all join condition links in the WHERE clause
List all search fields in the WHERE clause

23. Outer Joins
Limitation of inner joins: some records may be omitted if corresponding records don’t exist in one of the tables
Example: retrieve records for all students, along with their corresponding ENROLLMENT information

24. Outer Joins
Student 105 (Michael Connoly) does not have any ENROLLMENT records

25. Outer Joins
No records retrieved for Michael:

26. Outer Joins
To include records in first (inner) table, even when they do not have matching records in second (outer) table, place outer join marker (+) beside outer table name in join clause

27. Outer Joins
Outer join marker

28. Self Joins
Used to join a table to itself when the table has a hierarchical relationship

29. Self Joins
To create a self-join, you need to create a table alias, which gives an alternate name to the table so you can create a join condition
Syntax to create table alias in FROM clause:
FROM table1 alias1, table2 alias2

30. Self Joins
PARENT_PROJECT
SUB_PROJECT
PROJECT

31. Self Join Example

32. Inequality Joins
Join created by placing making join condition satisfy an inequality condition

33. Inequality Joins

34. Nested Queries Created when a sub-query is nested within a main query
Main query: first query listed in SELECT command
Sub-query: retrieves one or more values that specify the main query’s search condition

35. Nested Query Where Sub-query Returns a Single Value
Syntax:
SELECT column1, column2, …
FROM table1, table2, …
WHERE join conditions
AND search_column1 =
(SELECT column1
FROM table1, table2, …
WHERE search and
join conditions)
Sub-query
that returns
one value

36. Nested Query Where Sub-query Returns Multiple Values
Syntax:
SELECT column1, column2, …
FROM table1, table2, …
WHERE join conditions
AND search_column1 IN
(SELECT column1
FROM table1, table2, …
WHERE search and
join conditions)
Sub-query
that returns
multiple
values

37. Using Set Operators in Queries
Performs set operations on outputs of two unrelated queries
Both queries must have:
same number of display fields
corresponding display fields must have same data type

38. Query Set Operators UNION: combines results, suppresses duplicate rows
UNION ALL: combines results, displays duplicates
INTERSECT: finds matching rows
MINUS: returns the difference between returned record sets

39. Selecting Records For Update
In a normal SELECT command, the retrieved records are not locked, and are available for other users to view, updated, and delete
Sometimes, you need to select records, and then immediately update them based on the retrieved values
Airline seat reservations
Inventory items for sale

40. Selecting Records For Update
Syntax:
SELECT column1, column2, …
FROM table1, table2, …
WHERE search and join conditions
FOR UPDATE OF column1, column2, …
NOWAIT;

41. Selecting Records For Update
All retrieved records are locked until you issue a COMMIT command
Fields listed in FOR UPDATE clause are for documentation purposes only
NOWAIT clause is optional
Makes it so when another user tries to retrieved locked record, their system doesn’t just “hang”

42. Database Views Logical table based on a query
Does not physically exist in the database
Presents data in a different format from underlying tables
Uses:
Security
Simplifying complex queries

43. Database Views Creating a view: CREATE VIEW view_name AS SQL_command;
Views can be queried just like tables:
SELECT *
FROM view_name;

44. Simple Views
Based on SQL query that retrieves data from only one table
View can support all table operations:
INSERT
UPDATE
DELETE

45. Complex Views Based on query that retrieves data from multiple tables
Can only be used to support SELECT operations
No table operations supported

46. 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
SLName
ROWID
Brown
Jones
Smith
Helgeson

47. 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

48. 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

49. Creating Indexes Syntax: CREATE INDEX index_name
ON tablename(index_field);

50. Synonyms Alternate name for a table
Allows you to not have to preface table with owner’s username when you are querying a table that belongs to another user

51. Public Synonyms Can only be created by a DBA Syntax:
CREATE PUBLIC SYNONYM synonym_name
FOR owner_name.tablename;
All users with privileges to use table can then use synonym instead of owner_name.tablename

52. Private Synonyms
You can create private synonyms for any tables that you have privileges to use
Only you can use the synonym
Syntax:
CREATE SYNONYM synonym_name
FOR table_name.table_name;

53. End of Lecture