1. Outline: SQL DDL - creating schemas - contraints - modifying schemas
DML
- in separate lectures
DCL
TCL

2. SQL provides DDL capabilities for the conceptual and external levels
Data definition language (DDL): used to define the data schema. Ideally one schema definition language per level
SQL provides DDL capabilities for the conceptual and external levels
in practice there might be one for all levels

3. Data Manipulation language (DML): Used to manipulate data.
DBMS Languages
Data Manipulation language (DML): Used to manipulate data.
typical systems provide a general purpose language for inserting, updating, deleting, and retrieving data
two distinctions:
set-oriented
row-at-a-time (relation)
Sept. 2005

4. Introduction to SQL
SQL stands for Structured Query Language, which is used for to declare how information should be stored and retrieved from RDBMS.
A table (relation) is a primary database object of SQL that is used to store data.

5. SQL was invented and developed by IBM in early 1970’s.
SQL became a standard of the American National Standards Institute (ANSI) in 1986, and of the International Organization for Standardization (ISO) in  Since then, the standard has been revised to include a larger set of features. Despite the existence of such standards, though, most SQL code is not completely portable among different database systems without adjustments.
SQL89, SQL92, SQL1999, 2003, 06, 08, 11

6. Why SQL?
SQL is a very-high-level language, in which the programmer is able to avoid specifying a lot of data-manipulation details that would be necessary in languages like C++.
declarative or non-procedural

7. Benefits of SQL
Non-procedural language, because more than one record can be accessed rather than one record at a time.
It is common language for all relational databases. In other words it is portable and it requires very few modifications so that it can work on other databases.
Very simple commands for querying, inserting and modifying data and objects.

8. Case insensitive or sensitive
SQL commands themselves are case insensitive.
Values in ‘’ are case sensitive though.

9. Introduction to SQL(Cont’d)
In order to communicate with the database, SQL supports the following categories of commands:-
DDL, Data Definition Language- create, alter,drop commands.
DML, Data Manipulation Language- insert, select, delete and update commands.
TCL, Transaction Control Language- commit, savepoint and rollback commands.
DCL, Data Control Language- grant and revoke commands.

10. DDL
Data Definition Language (DDL) statements are used to define the database structure or schema. Some examples:
CREATE - to create objects in the database
ALTER - alters the structure of the database
DROP - delete objects from the database
TRUNCATE - remove all records from a table, including all spaces allocated for the records are removed
COMMENT - add comments to the data dictionary
RENAME - rename an object

11. DML
Data Manipulation Language (DML) statements are used for managing data within schema objects. Some examples:
INSERT - insert data into a table
UPDATE - updates existing data within a table
DELETE - deletes all records from a table, the space for the records remain
SELECT - retrieve data from the a database.
Even though select does not exactly change the instance of the a table, SELECT is still considered as an DML command.
The most important one actually
MERGE - UPSERT operation (insert or update)
CALL - call a PL/SQL or Java subprogram
EXPLAIN PLAN - explain access path to data
LOCK TABLE - control concurrency

12. ?
Difference between TRUNCATE, DELETE and DROP commands

13. DCL Non-navigational data access sub language
TCL
Data Control Language (DCL) statements. Some examples:
GRANT - gives user's access privileges to database
REVOKE - withdraw access privileges given with the GRANT command

14. TCL
Transaction Control (TCL) statements are used to manage the changes made by DML statements. It allows statements to be grouped together into logical transactions.
COMMIT - save work done
SAVEPOINT - identify a point in a transaction to which you can later roll back
ROLLBACK - restore database to original since the last COMMIT
SET TRANSACTION - Change transaction options like isolation level and what rollback segment to use
ROLLBACK is used for revoking the transactions until last commit. COMMIT is used for committing the transactions to the database.
Once we commit we cannot rollback. Once we rollback we cannot commit.
Need to understand what a user session is and what buffer is.
Caveats
Commit and Rollback are generally used to commit or revoke the transactions that are with regard to DML commands.
In general, if the changes return on the buffer it is possible to rollback not from the disk. Otherwise, for the changes will return on disk not on the buffer, it is impossible to rollback.
DML statements can be rollbacked where DDL are autocommit.
DML commands can't be rollback when a DDL command is executed immediately after a DML. DDL after DML means "auto commit".

15. Transactions
A sequence of one or more data manipulation statements that form a logical unit of work.
Either all statements are executed successfully or none are executed.
Example: A money transfer involving two accounts. In this case, at least two SQL statements need to go together as a unit.

16. Transaction Properties
Atomicity: a transaction is either entirely completed or aborted.
Consistency: the database must remain in a consistent state, before and after the transaction.
Isolation: The effects of one transaction should be transparent to other transactions, until committed.
Durability: changes by the transaction to recoverable resources are permanent.
Serialization: While a transaction is in progress, all required resources are locked to prevent other transactions from changing it.

17. Two fundamental groups of commands of Structured Query Language
DDL for data definition
Create, drop, alter …affecting schemas
DML for query, update, view, affecting data instances only
Manipulation (insert, delete, update)
Retrieval (select)
What makes SQL viable is that its queries are “optimized” quite well, yielding efficient query executions.

18. Oracle Internal Datatypes
Character datatypes:
- char datatype
- varchar2 datatype
- Long datatype
Number datatype
Date datatype
Raw datatype
Long raw datatype
LOB datatype

19. Data Definition Language
Create tables
SQL> CREATE TABLE <table_name>
( <column1_name> <data_type> <[not]null>,
<column2_name> <data_type> <[not]null>,
CONSTRAINT pk_name PRIMARY KEY (column_name);
CONSTRAINT fk_name FOREIGN KEY (column_name));
REFERENCE name1(name2) ON DELETE CASCADE);
Alter the existing table
SQL> ALTER TABLE <table_name> MODIFY/ADD (column definition);

20. Data Definition Language(Cont’d)
When there is no further use of records in a table and the structure has to be retained, then the records alone can be deleted. SQL>TRUNCATE table <table_name>;
Drop a table
SQL>DROP <table_name>;

21. Data manipulation Language
Insert a tuple into a table
SQL>INSERT <table_name> VALUES ( value_1, value_2,
value_3 ..);
Request for information stored in a table
SQL> SELECT column_names FROM table_name;
Change the existing records in the table SQL>UPDATE <table_name> SET <field>=value,….. WHERE condition;
Delete the rows in the table
SQL>DELETE FROM <table_name> WHERE condition;

22. Transaction Control Language
Transaction Changes can be made permanent to a database only by committing. Commit command is used to end a transaction and make the changes permanent.
SQL>COMMIT;
Savepoints are like markers to divide a very lengthy transaction to smaller ones.
SQL> SAVEPOINT savepoint_id;

23. Transaction Control Language(Cont’d)
Rollback command is used to undo the work done in the current transaction.
SQL> ROLLBACK ;
SQL> ROLLBACK TO SAVEPOINT savepoint_id;

24. Data Control language
Grant privilege command: Object privileges can be granted to others using the SQL command GRANT
SQL>GRANT privileges on<object_name> to <username>;
To withdraw the privilege that has been granted to a user, we use REVOKE command.
SQL>REVOKE privileges on<object_name> from <username>;

25. Other commands fall into groups for security, integrity constraints, transactions, embedding into other 3GLs such as C\c++, java, perl etc,
Security: Grant and Revoke are used to specify user privileges
Grant select, update on Employee to Diane;
Revoke update, delete on Works_on from Jim;
Embedded SQL: SQL can be placed within 3GL programs
Transactions: SQL systems implement the ACID properties

26. Defining Oracle8i Database Tables
To create a new table specify:
Table name
Name of each data field
Data type and size of each data field
Constraints: restrictions on the data values that a field can store

27. Create a Table CREATE TABLE table_name ( column_name1 data_type,)

28. Oracle naming standard
Series of rules Oracle Corporation established for naming all database objects. i.e. rules for names (table names, field names, or any names, etc.)
Objects must be from 1 to 30 characters long
Can contain letters, numbers, and the special symbols $, _, and #
Must begin with a character

29. Oracle8i Data Types
Data type: specifies the kind of data that a field stores, i.e., what type of data the column (attributes of a table) can hold.
Assigning a data type provides a means for error checking
Data types enable the DBMS to use storage space more efficiently by internally storing different types of data in different ways

30. Character Data Types VARCHAR2
Stores variable-length character data up to a maximum of 4,000 characters
Values in different records can have a different number of characters
Actually two parts, one is fixed length pointer, the other part is the real string part pointed by that pointer.
fieldname VARCHAR2(maximum_size)

31. Character Data Types CHAR
Fixed-length character data up to a maximum size of 2,000 characters
Data values for different records all have the same number of characters
DBMS adds trailing blank spaces to the end of the entry to make the entry fill the maximum_size value
Data longer than maximum_size causes an error
fieldname CHAR[(maximum_size)]

32. Character Data Types NVARCHAR2 and NCHAR
Analogous to VARCHAR2 and CHAR but use Unicode rather than ASCII
Used to hold character data in languages other than English

33. The most commonly used generic type is NUMBER.
Columns of type NUMBER can hold either an integer or a real number.

34. Number Data Types
Stores negative, positive, fixed, and floating point numbers between 10–130 and 10125, with precision up to 38 decimal places
General Syntax: fieldname NUMBER [([precision,] [scale])]
Integer: fieldname NUMBER(precision)
Fixed point: fieldname NUMBER[([precision],[scale])]
Floating point: fieldname NUMBER

35. Date and Time Data Types
Dates from December 31, 4712 BC to December 31, 4712 AD
Default format DD-MON-YY
Default time format HH:MI:SS A.M.
fieldname DATE
TIMESTAMP
Similar to DATE but stores fractional seconds
fieldname TIMESTAMP (fractional_seconds_precision)

36. Date and Time Data Types
INTERVAL YEAR TO MONTH
Time interval, expressed in years and months
specifies a positive time interval of 2 years and 11 months
fieldname INTERVAL YEAR[(year_precision)] TO MONTH
INTERVAL DAY TO SECOND
Time interval, expressed in days, hours, minutes, and seconds
-04 03:20:32.00: 4 days, 3 hours, 20 minutes, and 32 seconds
fieldname INTERVAL DAY[(leading_precision)] TO SECOND[(fractional_seconds_precision)]
Just need to know them, won’t be tested.

37. Example
This example demonstrates how you can create a table named "Person", with four columns, i.e. four attributes. The column names will be "LastName", "FirstName", "Address", and "Age":
CREATE TABLE Person  (
LastName varchar2(10),
FirstName varchar2(10),
Address varchar2(20),
Age int )

38. More detailed discussion on Oracle data types.

39. Definition of Data Integrity
a. Whether the data separated in different tables reflects and only reflects the mini-world facts, adhere to the facts, especially when data are pieced together from the separated tables, or all data in a table treated as a whole.

40. Types of Data Integrity
Different types of data integrity.
Nulls
It is about whether a single column allows or disallows inserts or updates of rows containing a null for the column.
Unique Column Values
About whether a column (or set of columns) allows only the insert or update of a row containing a unique value for the column (or set of columns).
Primary Key Values
Whether a column (or set of columns) so that each row in the table can be uniquely identified by the values in the column (or set of columns).
Referential Integrity
Whether a column (or set of columns) in one table that allows the insert or update of a row only if the value for the column or set of columns (the dependent value) matches a value in a column of a related table (the referenced value). Referential integrity also includes the rules that dictate what types of data manipulation are allowed on referenced values and how these actions affect dependent values. The rules associated with referential integrity include:
Restrict: A referential integrity rule that disallows the update or deletion of referenced data.
Set to Null: When referenced data is updated or deleted, all associated dependent data is set to NULL.
Set to Default: When referenced data is updated or deleted, all associated dependent data is set to a default value.
Cascade: When referenced data is updated, all associated dependent data is correspondingly updated; when a referenced row is deleted, all associated dependent rows are deleted.
Complex Integrity Checking
A column (or set of columns) allows or disallows inserts, updates, or deletes of a row based on the value it contains for the column (or set of columns). Larger, less in a range etc.

41. How Oracle Enforces Data Integrity
Oracle allows you to define and enforce each type of the data integrity (defined in the previous section.)using rules (constraints)
To auto the checking of data integrity, Oracle provides a set of rules for us to define on objects.
Each rule takes care of a type of data integrity concern.
Rules are there to use
But to use them usually is subject to the database administrator or application developer, limited by their technical background.

42. Constraints
Rules that restrict the data values that you can enter into a field in a database table
Integrity constraints: define primary and foreign keys
Value constraints: define specific data values or data ranges that must be inserted into columns and whether values must be unique or not NULL
Table constraint: restricts the data value with respect to all other values in the table
Field constraint: limits the value that can be placed in a specific field, irrespective of values that exist in other table records

43. Integrity Constraints
Define primary key fields
Specify foreign keys and their corresponding table and column references
Specify composite keys

44. Value Constraints
Check conditions: field value must be a specific value or fall within a range of values
NOT NULL constraints: specify whether a field value can be NULL
Default constraints: specify that a field has a default value that the DBMS automatically inserts for every record, unless the user specifies an alternate value
Unique constraints: specify that a field must have a unique value for every table record

45. Things the create table statement does!
When you create a table, you need to specify
Table name
Field name and data type for each field
Constraints as complete and reasonable as possible

46. DDL - creating schemas
Create table tablename …
constraints:
primary keys
foreign keys
on delete set null|cascade|set default
on update set null|cascade|set default
on insert set null|cascade|set default
uniqueness for secondary keys

47. On delete cascade
foreign key with a cascade delete means that if a record in the parent table is deleted, then the corresponding records in the child table with automatically be deleted.
This is called a cascade delete. A foreign key with a cascade delete can be defined in either a CREATE TABLE statement or an ALTER TABLE statement.
CREATE TABLE table_name (column1 datatype null/not null, column2 datatype null/not null, ... CONSTRAINT fk_column   FOREIGN KEY (column1, column2, ... column_n)   REFERENCES parent_table (column1, column2, ... column_n)   ON DELETE CASCADE );

48. CREATE TABLE products (
product_id numeric(10) not null,
supplier_id numeric(10) not null,
CONSTRAINT fk_supplier   FOREIGN KEY (supplier_id)  REFERENCES supplier(supplier_id)  
ON DELETE CASCADE );
Because of the cascade delete, when a record in the supplier table is deleted, all records in the products table will also be deleted that have the same supplier_id value.
This is one way to maintain data integrity.

49. We could also create a foreign key (with a cascade delete) with more than one field as in the example below.
CREATE TABLE supplier (
supplier_id numeric(10) not null,
supplier_name varchar2(50) not null,
contact_name varchar2(50),
CONSTRAINT supplier_pk PRIMARY KEY
(supplier_id, supplier_name) );
CREATE TABLE products
product_id numeric(10) not null,
CONSTRAINT fk_supplier_comp   FOREIGN KEY
(supplier_id, supplier_name)  REFERENCES supplier(supplier_id, supplier_name)  ON DELETE CASCADE
In this example, our foreign key called fk_foreign_comp references the supplier table based on two fields - the supplier_id and supplier_name fields.

50. Set null on delete for foreign key
What is a foreign key?
A foreign key means that values in one table must also appear in (come from) another table.
The referenced table is called the parent table while the table with the foreign key is called the child table. The foreign key in the child table will generally reference a primary key in the parent table.
A foreign key with a "set null on delete" means that if a record in the parent table is deleted, then the corresponding records in the child table will have the foreign key fields set to null. The records in the child table will not be deleted.
A foreign key with a "set null on delete" can be defined in either a CREATE TABLE statement or an ALTER TABLE statement.

51. DDL - Examples: Create table: Create table EMPLOYEENEW
(FNAME VARCHAR(15) NOT NULL,
MINIT CHAR(1),
LNAME VARCHAR(15) NOT NULL,
SSN CHAR(9) NOT NULL,
BDATE DATE,
ADDRESS VARCHAR(30),
SEX CHAR(1),
SALARY number(10, 2),
SUPERSSN CHAR(9),
DNO INT NOT NULL,
PRIMARY KEY(SSN),
/*constraint pk_en primary key(ssn), */
/*This allows you specify multiple column key words*/
FOREIGN KEY(SUPERSSN) REFERENCES EMPLOYEENEW(SSN),
FOREIGN KEY(DNO) REFERENCES DEPARTMENT(DNUMBER));

52. DDL - Examples: Specifying constraints: Create table EMPLOYEE (…,
DNO INT NOT NULL DEFAULT 1,
CONSTRAINT EMPPK
PRIMARY KEY(SSN),
CONSTRAINT EMPSUPERFK
FOREIGN KEY(SUPERSSN) REFERENCES EMPLOYEE(SSN)
ON DELETE SET NULL ON UPDATE CASCADE,
CONSTRAINT EMPDEPTFK
FOREIGN KEY(DNO) REFERENCES DEPARTMENT(DNUMBER)
ON DELETE SET DEFAULT ON UPDATE CASCADE);

53. set null or cascade: strategies to maintain data consistency
Employee
delete
ssn
supervisor
null
Employee
ssn
supervisor
null
not reasonable
delete
cascade
delete

54. set null or cascade: strategies to maintain data consistency
Employee
delete
ssn
supervisor
null
Employee
ssn
supervisor
reasonable
null
set null
null
delete

55. set default: strategy to maintain data consistency
Employee
ssn
DNO 4
change this
value to the
default value 1.
… …
Department
DNUMBER
… … 1
… …
… … 4
delete

56. Table Creation Sequence
When creating tables with foreign key references, create referenced tables first
Always create tables without foreign keys before those with foreign keys

57. drop table tablename …

58. Deleting Existing Table Records
TRUNCATE
Removes all of the table data without saving any rollback information
Must disable foreign key constraints before truncating table
TRUNCATE TABLE tablename;

59. Using an ALTER TABLE statement after the table has been created
Some records could have been there
The syntax for creating a primary key in an ALTER TABLE statement is:
ALTER TABLE table_name  add CONSTRAINT constraint_name PRIMARY KEY (column1, column2, ... column_n);

60. DDL - Examples: drop constraints ALTER TABLE EMPLOYEE
DROP CONSTRAINT EMPSUPERFK CASCADE;
ADD CONSTRAINT (EMPSUPERFK FOREIGN
KEY(SUPERSSN) REFERENCE EMPLOYEE(SSN));

61. DDL - modifying schemas
alter table tablename add|drop attributename cascade|restrict
alter table
ALTER TABLE EMPLOYEE
ADD JOB VARCHAR(12);
DROP ADDRESS CASCADE;
ALTER TABLE DEPARTMENT
ALTER MGRSSN DROP DEFAULT;
ALTER MGRSSN SET DEFAULT “ ”;

62. Modifying and Deleting Database Tables
Modify existing database tables by:
Changing the name of a table
Adding new columns
Deleting columns that are no longer needed
Changing the data type or maximum size of an existing column
Unrestricted action: some specifications can always be modified
Restricted action: specifications modified only in certain situations

63. Unrestricted Action

64. Restricted Actions

65. Deleting and Renaming Tables
To delete:
Drop table [tablename]
Use with caution
To delete foreign key constraints, add “cascade constraints”
To rename:
Rename old_tablename to new_tablename
DBMS automatically transfers to the new table integrity constraints, indexes, and privileges that referenced the old table.

66. Adding Fields to Existing Tables
To add a field:
ALTER TABLE tablename ADD(fieldname data_declaration constraints);

67. Modifying Existing Field Data Definitions
Can only change datatype to compatible data type (i.e. varchar2 to char)
ALTER tablename MODIFY(fieldname new_data_declaration);

68. Deleting a Field ALTER TABLE tablename DROP COLUMN fieldname;
Can be used to rename a field – first drop, then add

69. Adding and Deleting Constraints
Add a constraint: ALTER TABLE tablename ADD CONSTRAINT constraint_name constraint_definition;
Remove a constraint: ALTER TABLE tablename DROP CONSTRAINT constraint_name;

70. DML
DML
Insert
Update
Delete
Select
Discussed in a separate lecture