1. Lecture plan Oracle architecture SQL Data definition Queries
Insert, delete and update
Jane Reid, BSc/IT DB, QMUL, 28/1/02

2. Oracle Relational database Based on a client-server architecture
Each table column is independent and identified by name
Ordering of rows is unimportant
All operations should be relational, i.e. generate new relations from old ones
System supports at least one JOIN operation
Based on a client-server architecture
Jane Reid, BSc/IT DB, QMUL, 28/1/02

3. Oracle architecture Oracle server consists of: Database (raw data)
Logical structure = database schema
Physical structure = file structure
Instance (processes and system memory)
Jane Reid, BSc/IT DB, QMUL, 28/1/02

4. Logical database structure
Organised into:
Tablespaces
Schemas
Data blocks
Extents
Segments
Jane Reid, BSc/IT DB, QMUL, 28/1/02

5. Tablespaces Group related logical structures together
SYSTEM tablespace created automatically
Holds the data dictionary
Meta-data in machine-readable format
Includes security information, schema object information, space allocation, etc
May also have one or more user tablespaces
Each table belongs to a specific tablespace
Jane Reid, BSc/IT DB, QMUL, 28/1/02

6. Schemas
A named collection of schema objects associated with a particular user
Equivalent to a user’s personal space
Created automatically when a user account is set up
Jane Reid, BSc/IT DB, QMUL, 28/1/02

7. Data blocks Corresponds to a specific number of bytes of disk space
Size can be set for each database at creation
Jane Reid, BSc/IT DB, QMUL, 28/1/02

8. Extents
Specific number of contiguous data blocks allocated for storing a specific type of information
Jane Reid, BSc/IT DB, QMUL, 28/1/02

9. Segments A set of extents allocated for a certain logical structure
Oracle dynamically allocates extents to segments as existing extents fill up
Jane Reid, BSc/IT DB, QMUL, 28/1/02

10. Physical database structure
Consists of:
Datafiles (e.g. table and index data)
One or more datafiles form a tablespace
Redo log files (usually multiplexed)
Record all changes made to the data
Used in recovery
Control files (usually multiplexed)
Contain a list of all other files in the database
Jane Reid, BSc/IT DB, QMUL, 28/1/02

11. Oracle instance Consists of: Processes Shared memory used by processes
User processes
Oracle processes
Shared memory used by processes
Jane Reid, BSc/IT DB, QMUL, 28/1/02

12. User processes Manipulate the user’s input
Communicate with the Oracle server process
Display the information requested by the user
Jane Reid, BSc/IT DB, QMUL, 28/1/02

13. Oracle processes Perform functions for users:
Server processes handle requests from connected user processes
Background processes perform asynchronous I/O and provide increased parallelism
Jane Reid, BSc/IT DB, QMUL, 28/1/02

14. Shared memory [1]
Used for caching data, indexes and storing shared program code
Organised into memory structures of a fixed size created on instance startup:
System global area (SGA)
Used to store data and control information for one Oracle instance
Holds database buffer cache, redo log buffer and shared pool
Jane Reid, BSc/IT DB, QMUL, 28/1/02

15. Shared memory [2] Program global area
Used to store data and control information for the Oracle server processes
Jane Reid, BSc/IT DB, QMUL, 28/1/02

16. SQL Standard for commercial relational DBs
High-level declarative language interface
User specifies what the result should be
Optimisation and query execution decisions left to DBMS
Based on tuple relational calculus, with some relational algebra features
Jane Reid, BSc/IT DB, QMUL, 28/1/02

17. SQL versions Standard version accepted by ANSI / ISO
Current version is SQL3
Not all relational DBMSs support SQL3 (may support SQL-92, i.e. version 2)
Contains some object-oriented features
Jane Reid, BSc/IT DB, QMUL, 28/1/02

18. SQL in Oracle Oracle’s own version of SQL - SQLPlus
DDL and DML statements
View definition
Security and authorisation specification
Definition of integrity constraints
Transaction control specification
Session and system control statements
Embedding SQL into programming languages
Jane Reid, BSc/IT DB, QMUL, 28/1/02

19. Data definition Objects Commands Table CREATE ALTER DROP
Jane Reid, BSc/IT DB, QMUL, 28/1/02

20. Tables in SQL [1] Created by CREATE TABLE statement
CREATE TABLE EMPLOYEE
Known as base tables
Attributes ordered by creation order
Rows not ordered
Jane Reid, BSc/IT DB, QMUL, 28/1/02

21. Tables in SQL [2] CREATE TABLE specifies new relation by Relation name
Attributes
Name
Data type
Attribute constraints
Jane Reid, BSc/IT DB, QMUL, 28/1/02

22. Tables in SQL [3] Key/entity/referential integrity constraints
Can be specified in CREATE TABLE
Can be added later using ALTER TABLE
Table can be deleted by DROP TABLE statement
Jane Reid, BSc/IT DB, QMUL, 28/1/02

23. Data types [1] Numeric Character-string Integer: INTEGER Real: FLOAT
Fixed length: CHAR(n)
Varying length: VARCHAR(n) / VARCHAR2 (n)
Jane Reid, BSc/IT DB, QMUL, 28/1/02

24. Data types [2] DATE Has main components YEAR, MONTH, DAY
Also stores century, hour, minute, second
Has format DD-MON-YYYY
E.g. 05-FEB-2001
Jane Reid, BSc/IT DB, QMUL, 28/1/02

25. CREATE DOMAIN SSN_TYPE AS CHAR(9);
Like a type declaration
Advantages
Easier to change data type
Improves schema readability
Can have optional default specification
CREATE DOMAIN SSN_TYPE AS CHAR(9);
Jane Reid, BSc/IT DB, QMUL, 28/1/02

26. Attribute constraints
Specified by CONSTRAINT
Example constraint: NOT NULL
Should always be specified for primary keys
Constraint may be given optional name
Specified by CONSTRAINT <name>
Must be unique within a schema
Jane Reid, BSc/IT DB, QMUL, 28/1/02

27. Default values Specified by DEFAULT <value>
Used if no explicit value assigned to attribute
NULL unless otherwise stated
Jane Reid, BSc/IT DB, QMUL, 28/1/02

28. Table constraints [1] PRIMARY KEY UNIQUE (secondary key)
FOREIGN KEY (referential integrity)
Referential integrity constraints can be violated by
Insertion or deletion of tuples
Foreign key value modified
Jane Reid, BSc/IT DB, QMUL, 28/1/02

29. Table constraints [2] Referential triggered action
Can be added to foreign key constraint to cause automatic update ON DELETE
Options are SET NULL, CASCADE and SET DEFAULT
Jane Reid, BSc/IT DB, QMUL, 28/1/02

30. DROP TABLE DEPENDENT CASCADE CONSTRAINTS;
Option
CASCADE CONSTRAINTS
DROP TABLE DEPENDENT CASCADE CONSTRAINTS;
Jane Reid, BSc/IT DB, QMUL, 28/1/02

31. ALTER TABLE [1] Command which allows Adding column Dropping column
ALTER TABLE EMPLOYEE ADD JOB VARCHAR(12);
Dropping column
ALTER TABLE EMPLOYEE DROP ADDRESS CASCADE;
Jane Reid, BSc/IT DB, QMUL, 28/1/02

32. ALTER TABLE DEPARTMENT ALTER MGRSSN
Changing column definition (add/drop default)
ALTER TABLE DEPARTMENT ALTER MGRSSN
DROP DEFAULT;
SET DEFAULT ‘ ’;
Jane Reid, BSc/IT DB, QMUL, 28/1/02

33. ALTER TABLE [3] Adding / dropping table constraints
ALTER TABLE EMPLOYEE DROP CONSTRAINT EMPSUPERFK CASCADE;
ALTER TABLE EMPLOYEE ADD CONSTRAINT EMPSUPERFK;
FOREIGN KEY(SUPERSSN) REFERENCES EMPLOYEE(SSN)
ON DELETE SET NULL;
Jane Reid, BSc/IT DB, QMUL, 28/1/02

34. Queries SQL allows two or more identical tuples in a relation
Table is thus a multi-set / bag of tuples
Table can be constrained to be a set by
Use of a key constraint
DISTINCT option
Jane Reid, BSc/IT DB, QMUL, 28/1/02

35. SELECT statement [1] Basic syntax is SELECT <attribute list>
FROM <table list>
WHERE <condition>
Jane Reid, BSc/IT DB, QMUL, 28/1/02

36. SELECT statement [2] Example - query 0
Similar effect to relational algebra SELECT-PROJECT combination
SELECT clause specifies projection attributes
WHERE clause specifies selection condition
SQL may retrieve duplicate tuples, however
Jane Reid, BSc/IT DB, QMUL, 28/1/02

37. SELECT statement [3] Example - query 1
Similar effect to relational algebra SELECT-PROJECT-JOIN combination
SELECT clause specifies projection attributes
WHERE clause specifies selection condition
Condition DNUMBER = DNO is join condition
Jane Reid, BSc/IT DB, QMUL, 28/1/02

38. SELECT statement [4] Example - query 2
Multiple select and join conditions possible
Jane Reid, BSc/IT DB, QMUL, 28/1/02

39. Ambiguous attribute names
Attributes with same name in different relations
Names must be qualified with relation name
Example - query 1A
Jane Reid, BSc/IT DB, QMUL, 28/1/02

40. Aliasing [1] Queries can refer to same relation twice
One-level recursive query
Not possible to have infinitely recursive query
Aliases / tuple variables can be declared
Example - query 8
Jane Reid, BSc/IT DB, QMUL, 28/1/02

41. EMPLOYEE AS E (FN, MI, LN, SSN, BD, ADDR, SEX, SAL, SSSN, DNO)
Aliasing [2]
Also possible to rename relation attributes
EMPLOYEE AS E (FN, MI, LN, SSN, BD, ADDR, SEX, SAL, SSSN, DNO)
This ‘shorthand’ can be used in any query
Example - query 1B
Jane Reid, BSc/IT DB, QMUL, 28/1/02

42. No WHERE clause No condition on tuple selection Example - query 9
More than one relation in FROM clause means cross product
Example - query 10
Similar to relational algebra cross product - PROJECT combination
Jane Reid, BSc/IT DB, QMUL, 28/1/02

43. Use of asterisk Used to retrieve all attribute values in SELECT clause
Examples - queries 1C, 1D, 10A
Jane Reid, BSc/IT DB, QMUL, 28/1/02

44. Tables as sets [1] Duplicate elimination not automatic
Expensive
Sometimes unnecessary or unwise
Not suitable for use with aggregate functions
Can be achieved by DISTINCT in SELECT clause
Example - queries 11, 11A
Jane Reid, BSc/IT DB, QMUL, 28/1/02

45. Tables as sets [2]
Set union (UNION) and other set operations sometimes available, e.g. EXCEPT, CONTAINS, but are non-standard
Example - queries 3, 4
Jane Reid, BSc/IT DB, QMUL, 28/1/02

46. Substring comparison Uses LIKE comparison operator
% replaces any number of characters
_ replaces a single character
Examples - queries 12, 12A
Jane Reid, BSc/IT DB, QMUL, 28/1/02

47. Arithmetic operators Standard arithmetic operators can be applied
Example - query 13
Jane Reid, BSc/IT DB, QMUL, 28/1/02

48. Other operators String concatenation || Numeric value range BETWEEN
Example - query 14
Ordering by value of one or more attributes
Example - query 15
Jane Reid, BSc/IT DB, QMUL, 28/1/02

49. Nested queries [1]
Complete SELECT-FROM-WHERE block inside WHERE of outer query
Ambiguity among attributes of same name
Assumed they belong to relation in innermost nested query
Correlated queries
Condition in inner WHERE references “outer” attribute
Jane Reid, BSc/IT DB, QMUL, 28/1/02

50. Nested queries [2]
Queries with nested SELECT-FROM-WHERE blocks using IN can usually be expressed as single block query
Example - query 4A
Jane Reid, BSc/IT DB, QMUL, 28/1/02

51. Set comparison [1] Comparison operator IN / NOT IN can compare
Value with multi-set of values
Tuple of values with multi-set of union-compatible tuples
Jane Reid, BSc/IT DB, QMUL, 28/1/02

52. Set comparison [2] SELECT DISTINCT ESSN FROM WORKS_ON
WHERE (PNO, HOURS) IN (SELECT PNO, HOURS
FROM WORKS_ON
WHERE SSN = ‘ ’);
Jane Reid, BSc/IT DB, QMUL, 28/1/02

53. Other comparison operators
>, >=, <, <=, <>
Can be used with ANY, SOME, ALL
SELECT LNAME, FNAME
FROM EMPLOYEE
WHERE SALARY > ALL (SELECT SALARY
FROM EMPLOYEE WHERE DNO = 5);
Jane Reid, BSc/IT DB, QMUL, 28/1/02

54. Functions in SQL EXISTS / NOT EXISTS UNIQUE Evaluates to Boolean value
Indicates if result of a correlated, nested query is empty
Example - queries 16B, 6, 7
UNIQUE
Indicates if there are duplicate tuples
Jane Reid, BSc/IT DB, QMUL, 28/1/02

55. WHERE clause variations
Explicit set of values
Example - query 17
Use of NULL
Used with IS / IS NOT
Equality comparison (=) not appropriate
Example - query 18
Jane Reid, BSc/IT DB, QMUL, 28/1/02

56. Aggregate functions Built-in functions
COUNT
SUM
MAX
MIN
AVG
Example - queries 19, 20, 21, 22, 23, 5
Jane Reid, BSc/IT DB, QMUL, 28/1/02

57. GROUP BY clause Group tuples with same value for an attribute
E.g. for averaging across categories of tuples (rather than across all tuples)
Example - query 24, 25
Jane Reid, BSc/IT DB, QMUL, 28/1/02

58. HAVING clause
Places condition on selection of tuple groups specified by GROUP BY clause
Example - queries 26, 28
Jane Reid, BSc/IT DB, QMUL, 28/1/02

59. Summary of SQL queries [1]
SELECT <attribute and function list>
FROM <table list>
[WHERE <condition>]
[GROUP BY <grouping attribute(s)>]
[HAVING <group condition>]
[ORDER BY <attribute list>]
Jane Reid, BSc/IT DB, QMUL, 28/1/02

60. Summary of SQL queries [2]
Order of conceptual evaluation
FROM clause
WHERE clause
GROUP BY clause
HAVING clause
ORDER BY clause
SELECT clause
Jane Reid, BSc/IT DB, QMUL, 28/1/02

61. INSERT [1] Possible to insert Specify Example - update 1 Single tuple
Multiple tuples
Specify
Relation name
List of values for the tuple
In same order as attributes specified
Example - update 1
Jane Reid, BSc/IT DB, QMUL, 28/1/02

62. INSERT [2] Can specify limited subset of attributes
Must include all NOT NULL / non-default ones
Example - update 1A
DBMS may not enforce all integrity constraints
User must enforce the others
Examples - updates 2, 2A
Jane Reid, BSc/IT DB, QMUL, 28/1/02

63. DELETE Possible to delete
Single tuple
Multiple tuples
Tuples in other tables may be deleted by referential triggered action
Includes WHERE clause
Examples - updates 4A, 4B, 4C
Jane Reid, BSc/IT DB, QMUL, 28/1/02

64. UPDATE [1] Possible to modify attribute values of
Single tuple
Multiple tuples
Tuples in other tables may be modified by referential triggered action
Jane Reid, BSc/IT DB, QMUL, 28/1/02

65. UPDATE [2] Includes Example - updates 6, 5 WHERE clause
SET clause, which specifies
Attributes to be modified
New attribute values (NULL / DEFAULT possible)
Example - updates 6, 5
Jane Reid, BSc/IT DB, QMUL, 28/1/02

66. Views Simplifies query specification Always up-to-date
Virtual tables derived from defining tables
Other virtual table(s)
Base tables(s)
Jane Reid, BSc/IT DB, QMUL, 28/1/02

67. Creating views View definition includes Created using CREATE VIEW
Name
List of attribute names
Query to specify contents
Created using CREATE VIEW
Examples - view 1, 2
Jane Reid, BSc/IT DB, QMUL, 28/1/02

68. Querying and deleting views
SQL queries can be specified on views
Example - query view 1
Deleted using DROP VIEW
Example - view 1A
Jane Reid, BSc/IT DB, QMUL, 28/1/02

69. Updating views [1] View update often ambiguous Example - update view 1
DBMS may choose best option
User may be asked to specify preferred options during view definition
Example - update view 1
Jane Reid, BSc/IT DB, QMUL, 28/1/02

70. Updating views [2]
View with single defining table is updatable if view attributes contain primary key
Not possible to update
View defined on multiple queries using joins
View defined using grouping / aggregate functions
Jane Reid, BSc/IT DB, QMUL, 28/1/02

71. Assertions [1]
More general constraints can be specified via declarative assertions
Created using CREATE ASSERTION
Deleted using DROP ASSERTION
Jane Reid, BSc/IT DB, QMUL, 28/1/02

72. Assertions [2] CHECK clause can be used with CREATE DOMAIN statement
CREATE ASSERTION SALARY_CONSTRAINT
CHECK (NOT EXISTS (SELECT * FROM EMPLOYEE E, EMPLOYEE M, DEPARTMENT D
WHERE E.SALARY > M.SALARY AND
E.DNO = D.DNUMBER AND
D.MGRSSN = M.SSN) );
CHECK clause can be used with CREATE DOMAIN statement
CREATE DOMAIN D_NUM AS INTEGER
CHECK (D_NUM > 0 AND D_NUM < 21);
Jane Reid, BSc/IT DB, QMUL, 28/1/02