Chapter 2: Creating and Modifying Database Tables

IS421 DB Applications Mr. Ashraf Yaseen 1

Chapter 2:Creating and ModifyingDatabase Tables


Objectives

Become acquainted with Structured Query Language (SQL)

Learn about Oracle10g user schemas Learn how to define Oracle10g

database tables Create database tables using SQL*Plus


Objectives (cont.)

Learn how to debug Oracle10g SQL commands and use Oracle Corporation online help resources

Learn how to view information about your database tables using Oracle10g data dictionary views

Modify and delete database tables using SQL*Plus


Database Objects and Queries An Oracle database consists of multiple user accounts Each user account owns database objects

Tables Views Stored programs Etc.

• Query: command to perform operation on database object

• Structured Query Language (SQL) Industry standard query language for most of relational databases


Basic SQL Concepts and CommandsSQL (Structured Query Language) is used to manipulate the database.

There are two basic types of SQL commands:

DDL commands work with the structure of the objects (tables, indexes, views) in the database.

DML commands work with the data in the database (i.e.,manipulate the data).

Data Definition Language (DDL)

Data Manipulation Language (DML)


DDL Commands

Used to create and modify the structure of database objects CREATE ALTER DROP GRANT REVOKE

DDL commands execute as soon as they are issued, and do not need to be explicitly saved


DML Commands

Used to insert, view, and modify database data INSERT UPDATE DELETE SELECT

DML commands need to be explicitly saved or rolled back COMMIT ROLLBACK SAVEPOINT


Security -Granting Table Privileges Security is the prevention of unauthorized access to

the database. Within an organization, the database administrator determines the types of access various users need for the database.

Some users might be able to retrieve and update data in the database. Other users might be able to retrieve any data from the database but not make any changes to it. Still other users might be able to access only a portion of the database.


Oracle10g User Accounts

User account - identified by a unique username and password

User schema - all of the objects that the user creates and stores in the database

Object owner has privileges to perform all possible actions on an object


Oracle SQL command line utility for issuing SQL commands

Starting SQL Plus

Break Time: SQL Plus

LOGON to YOUR Oracle Account


How to Access Your Oracle Account

User Name:

Password:

Host string:

1. Click the START button, point to Programs2. Select Oracle –Oracle10g, then3. Click Application Development, then4. Select SQL PLUS


Types of Database Privileges

System Privileges Control the operations that the user can perform within the

database Create user accounts Connecting to the database, creating new tables, shutting

down the database, etc. Object Privileges

Granted on individual database objects Controls operations that a user can perform on a specific

object (insert data, delete data, etc.) When you create an object in your user schema, you can

then grant object privileges on that object to other database users


Creating New User Accounts

Done by DBA Syntax:

CREATE username IDENTIFIED BY password;


Defining Oracle10g Database Tables To create a table, you must specify:

Table name Field names Field data types Field sizes Constraints

restrictions on the data values that a field can store


Creating a Table

CREATE TABLE tablename

(fieldname1 data_type,

(fieldname2 data_type,

…)


Oracle Naming standers and Conventions

• From 1 to 30 characters

• Only alphanumeric characters, and special characters ($ , _, #)

• Must begin with a letter and can not contain blank spaces or hyphens Are the following names valid? Why?

customer ordercustomer-order#order

Naming standards are Series of rules Oracle Corporation established for naming all database objects


Oracle10g Data Types

Data type: specifies the kind of data that a field stores

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


Data Types

• Built-in provided by the system

• Library built by the software

vendor or a third party

• User-defined built by users


• Data type: specifies type of data stored in a field Date, character, number, etc.

• Uses/Purposes Error checking Efficient use of storage space

Oracle Data Types

L


Basic Built-In Data Types

• Character VARCHAR2 CHAR NVARCHAR2 / NCHAR

• Numeric NUMBER

• Date/Time

• Others: LONG, RAW, LONG RAW, BLOB


Character Data Types

1. 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 fieldname VARCHAR2(maximum_size)

(e.g.) emp_name VARCHAR2(20); an instance: ‘Jason Chen’


Character Data Types (cont.) 2. CHAR

Fixed-length character data (<= 2000 characters) default is 1 if no field size is specified 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)]

pros: use data storage space more efficiently and processed faster cons: causes inconsistent query results in other Oracle applications

e.g. s_class CHAR(2); ‘SR’ ‘JR’ ‘SO’ ‘FR’ ‘GR’

s_state CHAR(2) DEFAULT ‘WI’; student_gender CHAR;

[optional]


Character Subtypes

Examples:

VARCHAR2(5) ‘Smith’ or ‘Smi’

CHAR(5) ‘Smith’ or ‘Smi ’


Question: Which query will possibly generate student information?

What data type should be used if there is any chance that all column spaces will NOT be filled?

Answer: VARCHAR2

s_last VARCHAR2(15);

SELECT s_last, s_first, s_addressFROM studentWHERE s_last = ‘Smith’;

s_last CHAR(15);

SELECT s_last, s_first, s_addressFROM studentWHERE s_last = ‘Smith’;

L


When use Query:

SELECT s_last, s_first, ssn, telephone FROM student

WHERE s_last = ‘Smith’;

Case is sensitive within the single

quotation. SQL Plus commands are NOT case

sensitive, but Query within the single quotation are case sensitive.


Character Data Types (cont.)

3. NVARCHAR2 and NCHAR Analogous to VARCHAR2 and

CHAR but use Unicode rather than ASCII

Used to hold character data in languages other than English


4. Number Data Types Stores negative, positive, fixed, and floating point

numbers between 10 -130 and10 +125 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


Number Data Types (examples) a) Integer: Number (n)

e.g. s_id NUMBER(5) 12345

b) Fixed-point numbers e.g. current_price NUMBER (5, 2);

259.99 33.89 c) Fixed-point numbers (cont.)

e.g. total_mileage NUMBER (5, 1); 259.9 33.8

d) Floating-point Number – with a variable number of decimal places e.g. s_gpa NUMBER;

3.89 2.7569 3.2


5. Date and Time Data Types DATE

Dates from December 31, 4712 BC to December 31, 4712 AD

Stores the century, year, month, day, hour, minute and second.

Default format DD-MON-YY Default time format HH:MI:SS A.M.

fieldname DATE Sample declaration: s_dob DATE;Use one of the following format masks:

TO_DATE (‘ ’, ‘MM/DD/YY’) TO_DATE (‘ ‘, ‘DD-MON-YYYY’) TO_DATE (‘ ‘, ‘HH:MI AM’)


Date and Time Data Types (cont.) TIMESTAMP

Similar to DATE but stores fractional seconds

fieldname TIMESTAMP (fractional_seconds_precision)

If you omit the fractional_seconds_precision specification, the default value is 6 decimal places.

E.g: s1_date_received TIMESTAMP(2);


Date and Time Data Types (cont.)

INTERVAL YEAR TO MONTH Time interval, expressed in years and months +02-11 specifies a positive time interval of 2 years and 11 months fieldname INTERVAL YEAR[(year_precision)] TO MONTH e.g., Software Expert database (p.48) elapsed_time INTERVAL YEAR(2) 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)] e.g. DDL:

elapsed_time INTERVAL DAY(6) TO SECOND, DML:

TO_DSINTERVAL('53 00:00:00.00')


6. Large Object (LOB) Data Types


What is a Constraint?

A rule that restricts the values that can be inserted into a field

A mechanism used to protect the relationship between data within an Oracle

table, or the correspondence between data in two different

tables. For example, the state entered must be one of the 50

states in the U.S.


Types of Constraints

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


Creating a Table

CREATE TABLE tablename(fieldname1 data_type [CONSTRAINT constraint_name]

CONSTRAINT_TYPE,fieldname2 data_type [CONSTRAINT constraint_name]

CONSTRAINT_TYPE,,…)

CREATE TABLE tablename(fieldname1 data_type,fieldname2 data_type,

[CONSTRAINT constraint_name] CONSTRAINT_TYPE(coulmn_name));


I. Naming conventions for constraints

<tablename>_<fieldname>_<constraint id>

Where <constraint id> is:• pk PRIMARY KEY• fk REFERENCES <tablename> (pk)• • cc CHECK <condition to be checked>

(note that cc stands for CHECKCONDITION)

• nn NOT NULL• uk UNIQUE

Inte

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con

stra

int

Val

ue

con

stra

int

e.g., s_id NUMBER (6) CONSTRAINT student_s_id_pk PRIMARY KEY;


Oracle Constraint Naming Convention tablename_ fieldname_constraintID


Integrity Constraints

Define primary key fields

Specify foreign keys and their corresponding table and column references

Specify composite keys


Table-level Can be defined when field is declared Syntax:

CONSTRAINT constraint_name PRIMARY KEY

Primary Key Constraints

SQL> CREATE TABLE my_students2 (s_id NUMBER(6) CONSTRAINT my_students_s_id_pk PRIMARY KEY,3 s_name VARCHAR2(30),4 s_class CHAR(2),5 s_dob DATE);


Can also be defined after all table field definitions are completed

Primary Key Constraints (cont.)

SQL> CREATE TABLE my_students2 (s_id NUMBER(6), 3 s_name VARCHAR2(30),4 s_class CHAR(2),5 s_dob DATE),6 CONSTRAINT student_s_id_pk PRIMARY KEY (s_id));

SQL> CREATE TABLE my_students2 (s_id NUMBER(6) CONSTRAINT my_students_s_id_pk PRIMARY KEY,3 s_name VARCHAR2(30),4 s_class CHAR(2),5 s_dob DATE);


Primary Key Constraints (cont.)

You will learn how to create the following SQL (DDL) command:

CREATE TABLE location(loc_id NUMBER(6),bldg_code VARCHAR2(10),room VARCHAR2(6),capacity NUMBER(5),CONSTRAINT location_loc_id_pk PRIMARY KEY (loc_id));


Table-level Can only be defined after field is defined as a

primary key in another table Syntax:

CONSTRAINT constraint_name

REFERENCES primary_key_table_name (field_name)

Foreign Key Constraints


Can be defined when field is declared

Foreign Key Constraints

N

CREATE TABLE faculty(f_id NUMBER(6) CONSTRAINT faculty_f_id_pk PRIMARY KEY(f_id),f_last VARCHAR2(30),f_first VARCHAR2(30),f_mi CHAR(1),loc_id NUMBER(5) CONSTRAINT faculty_loc_id_fk REFERENCES location(loc_id)f_phone VARCHAR2(10),f_rank VARCHAR2(8),f_pin NUMBER(4),f_image BLOB, );

SQL> SELECT TABLE_NAME FROM USER_TABLES;


Can also be defined after all table field definitions are completed

Foreign Key Constraints (cont.)

CREATE TABLE faculty(f_id NUMBER(6),f_last VARCHAR2(30),f_first VARCHAR2(30),f_mi CHAR(1),loc_id NUMBER(5),f_phone VARCHAR2(10),f_rank VARCHAR2(8),f_pin NUMBER(4),f_image BLOB, CONSTRAINT faculty_f_id_pk PRIMARY KEY(f_id),CONSTRAINT faculty_loc_id_fk FOREIGN KEY (loc_id) REFERENCES location(loc_id));

SQL> SELECT TABLE_NAME FROM USER_TABLES;


Column-level Restricts data values that can be inserted in a

field In general, avoid value constraints because

they make the database very inflexible

Value Constraints


Types of Value Constraints Check condition: restricts to specific values

CONSRAINT student_s_class_cc CHECK ((s_class='FR') OR (s_class='SO') OR (s_class='JR') OR (s_class=’SR'));

CONSTRAINT course_credits_cc CHECK ((credits>0) AND (credits <=18));

s_gender (M or F)CONSTRAINT my_students_s_gender_cc CHECK (s_gender = ‘M’) OR (s_gender = ‘F’);

Not NULL: specifies that a field cannot be NULL Must be created in column declaration. s_last VARCHAR2(30) CONSTRAINT

student_s_last_nn NOT NULL; CONSTRAINT my_students_s_dob_nn NOT NULL;


Types of Value Constraints (cont.) Unique

Table constraint Specifies that a non-primary key field must have a unique

value CONSTRAINT term_term_desc_uk UNIQUE (term_desc);

Default: specifies a default value that is inserted automatically Must be created in the column declaration s_state CHAR(2) DEFAULT ‘WI’;


Summary on Value Constraints (cont.)

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


Creating Database Tables Using SQL*Plus Type SQL commands at the SQL prompt

End each command with a semicolon (;)

Not case sensitive


Log On to SQL*Plus

Oraclelab


Create a Table


Using Notepad

Useful to use Notepad to edit sql commands Commands can be edited without

retyping Commands can be saved Saving multiple sql commands in a

file creates a script


Study …

Can you create TABLE student now?


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


Errors - Oracle Help Resources

When an error occurs error information is displayed: Line number Position on line Error code Description of error

Error codes 3 letter prefix (I.e. ORA) 5 digit code More information on errors can be found at

http://otn.oracle.com


Syntax:CONSTRAINT constraint_name PRIMARY KEY (field1, field2) Must be defined after fields that composite key are

defined

Composite Primary Keys

CREATE TABLE ENROLLMENT(s_id NUMBER(6),c_sec_id NUMBER(6),grade CHAR(1), CONSTRAINT enrollment_pk PRIMARY KEY (s_id, c_sec_id),CONSTRAINT enrollment_sid_fk FOREIGN KEY (s_id) REFERENCES student(s_id),CONSTRAINT enrollment_csecid_fk FOREIGN KEY (c_sec_id) REFERENCES course_section (c_sec_id));


Integrity and Value Constraints: Other Examples (cont.)

CREATE TABLE faculty(f_id NUMBER(6) CONSTRAINT faculty_f_id_pk PRIMARY KEY,f_last VARCHAR2(30) CONSTRAINT faculty_f_last_nn NOT NULL,f_first VARCHAR2(30) CONSTRAINT faculty_f_first_nn NOT NULL,f_mi CHAR(1),loc_id NUMBER(5) CONSTRAINT faculty_loc_id_fk REFERENCES location(loc_id),f_phone VARCHAR2(10),f_rank VARCHAR2(8) CONSTRAINT faculty_f_rank_ccCHECK ((f_rank = ’INST') OR (f_rank = ’ASST')OR (f_rank = 'ASSO') OR (f_rank = ’FULL')),f_pin NUMBER(4) CONSTRAINT faculty_f_pin_uk UNIQUE,f_image BLOB);


Exiting SQL*Plus

Three ways to exit SQL*Plus: Type exit at the SQL prompt lick File on the menu bar, and then click Exit Click the Close button on the program window title

bar Database session ends when SQL*Plus exits


Viewing Information About Tables describe tablename: displays short description about

tablename; column names, NOT NULL columns and data types.

Data dictionary: tables that contain information about the structure of the database. When the DBA creates a new DB, the system creates the data

dictionary in a user schema named SYS. Oracle10g DBMS automatically updates the data dictionary

tables as users create, update, or delete database objects. Users do not directly interact with data dictionary tables, They interact with the data dictionary views.

View: is a db object that the DBMS bases on an actual db table and which enables the DBMS to present the table data in a different format based on user needs. It can serve to hide some table columns in which the user has no interest or doesn’t have privileges to view.


Viewing Information About Tables Categories of Data Dictionary Views:

USER: shows the objects in the current user’s schema ALL: shows both objects in the current user’s schema

and objects that the user has privileges to manipulate DBA: allows users who are database administrators to

view information about all database objects

General command:SELECT view_columnname1, view_columnname2, …FROM prefix_object;


Database Objects with Data Dictionary View Object NameObject Type

OBJECTSAll database objects

TABLESDatabase tables

INDEXESTable indexes created to improve query performance

VIEWSDatabase views

SEQUENCESSequences created to automatically generate surrogate key values

USERSDatabase users

CONSTRAINTSTable constraints

CONS_COLUMNSTable columns that have constraints

IND_COLUMNSIndexed columns

TAB_COLUMNSAll table columns


Viewing Tables in the Database


Viewing Constraints on One Table


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


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.

Views and stored program units that reference the old table name become Invalid.


Adding Columns to Existing Tables To add a field:

ALTER TABLE tablename ADD(fieldname data_declaration constraints);

Example:ALTER TABLE faculty ADD (start_date DATE);


Modifying Existing Column Data Definitions Can only change datatype to compatible data

type (i.e. varchar2 to char)

ALTER tablename

MODIFY(fieldname new_data_declaration);

Example:ALTER TABLE faculty MODIFY (f_rank VARCHAR2 (4));


Deleting a Column To delete a field

ALTER TABLE tablename

DROP COLUMN fieldname;

Examples:ALTER TABLE faculty DROP COLUMN f_rank;

ALTER TABLE faculty ADD (faculty_rank VARCHAR2(4));


Renaming a Column To rename a field


RENAME COLUMN old_fieldname TO new_fieldname;


Adding and Deleting Constraints Add a constraint:


ADD CONSTRAINT constraint_name constraint_definition;

Remove a constraint:ALTER TABLE tablename

DROP CONSTRAINT constraint_name;

Examples:ALTER TABLE facultyADD CONSTRAINT faculty_f_pin_uk UNIQUE (f_pin);

ALTER TABLE facultyDROP CONSTRAINT faculty_f_pin_uk;


Enabling and Disabling Constraints When modifying a database it can be useful to disable

constraints Constraints are enabled by default To disable a constraint:


DISABLE CONSTRAINT constraint_name; To enable a constraint:


ENABLE CONSTRAINT constraint_name;

ALTER TABLE facultyDISABLE CONSTRAINT faculty_loc_id_fk;

ALTER TABLE facultyENABLE CONSTRAINT faculty_loc_id_fk;

DROP TABLE faculty CASCADE CONSTRAINTS;

EXIT;


SQL Commands

CREATE TABLE <tablename> … ; DROP TABLE <tablename>; RENAME <tablename>TO<newtablename>;

Use the following commands to check your tables SELECT table_name FROM user_tables; DESCRIBE <tablename>;


SQL Commands

SELECT constraint_name

FROM user_constraints;

SELECT constraint_name

FROM user_constraints

WHERE TABLE_NAME =‘<tablename>’;

‘case sensitive’ within the quotation


SQL Commands (cont.)

ALTER TABLE <tablename>

ADD <fieldname> <data declaration>; ALTER TABLE <tablename>

ADD/MODIFY <fieldname> <data declaration>

CONSTRAINT <integrity constraints>

CONSTRAINT <value constraints>;

EXIT; or QUIT;


Summary SQL commands include:

Data description language (DDL) commands: create, modify, Deleted database objects

Data manipulation language (DML) commands: insert, update, delete, view database data

To create a table: specify the table name, the name of each data field,

and the data type and size of each data field Data types ensure correct data values Constraints restrict values of database fields SQL*Plus commands are not case sensitive


Summary (cont.)

Errors include line number, position, error code

Use DESCRIBE command to display a table’s fieldnames and data types

Tables can be modified or deleted but some changes are restricted

Documents

Chapter 2: Creating and Modifying Database Tables