Database Systems Creating and Modifying Database Objects 1

Database Systems Creating and Modifying Database Objects 1

Database Objects n n An Oracle database consists of multiple user accounts Each user account owns database objects n n Tables Views Stored programs Etc. 2

Database Queries § Query: command to perform operation on database object § Create § Modify § View § Delete § Structured Query Language (SQL) § Standard query language for relational databases 3

SQL Command Types n Data Definition Language (DDL) n n Used to create and modify the structure of database objects Data Manipulation Language (DML) n Used to insert, update, delete, and view database data 4

DDL Commands n Used to create and modify the structure of database objects n n CREATE ALTER DROP DDL commands execute as soon as they are issued, and do not need to be explicitly saved 5

DML Commands n Used to insert, view, and modify database data n n n INSERT UPDATE DELETE SELECT DDL commands need to be explicitly saved or rolled back n n COMMIT ROLLBACK 6

User Accounts n Each Oracle database user has a user schema n n n Area in the database where the user’s database objects are stored Identified by a unique username and protected by a password Each user schema is granted specific privileges 7

Types of Database Privileges n System Privileges n Control the operations that the user can perform within the database n n Connecting to the database, creating new tables, shutting down the database, etc. Object Privileges n n n 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 8

Oracle Naming Standard n Oracle database objects must adhere to the Oracle Naming Standard n n n 1 to 30 characters long Must begin with a character Can contain characters, numbers, and the symbols $, _, and # 9

Creating New User Accounts n n Done by DBA Syntax: CREATE username IDENTIFIED BY password; 10

Example Oracle System Privileges Privilege Level Purpose CREATE SESSION User Connecting to database CREATE TABLE User Creating tables in current user schema DROP TABLE User Dropping tables in current user schema UNLIMITED TABLESPACE User Allows user to create schema objects using as much space as needed CREATE USER DBA Creating new users GRANT ANY PRIVILEGE DBA Granting system privileges to users CREATE ANY TABLE DBA Creating tables in any user schema DROP ANY TABLE DBA Dropping tables in any user schema 11

Granting System Privileges n n Done by DBA Syntax: GRANT privilege 1, privilege 2, … TO username; 12

Database Roles n n n Role is a database object that can be assigned system privileges Role is then assigned to a user, and the user inherits the role’s privileges Used to easily assign groups of related privileges to users 13

Creating Roles Syntax: CREATE ROLE role_name; n 14

Assigning Privileges to a Role n Syntax: GRANT privilege 1, privilege 2, … TO role_name; 15

Assigning a Role to a User Syntax: GRANT role_name TO user_name; n 16

Revoking System Privileges n Syntax: REVOKE privilege 1, privilege 2, … FROM username; 17

Administering System Privileges n To be able to grant system privileges to other users, a user account must have been granted the privilege WITH ADMIN OPTION 18

Defining Database Tables § To create a table, you must specify: § Table name § Field names § Field data types § Field sizes § Constraints 19

Table and Field Names § Must follow the Oracle Naming Standard § Each table in a user schema must have a unique name within that user schema § Each field in a table must have a unique name within that table 20

Oracle Data Types § Data type: specifies type of data stored in a field § Date, character, number, etc. § Uses § Error checking § Efficient use of storage space 21

Oracle Character Data Types § VARCHAR 2 § § Variable-length character strings Maximum of 4, 000 characters Must specify maximum width allowed No trailing blank spaces are added § Example declaration: student_name VARCHAR 2(30) 22

Character Data Types § CHAR § § Fixed-length character data Maximum size 2000 characters Must specify maximum width allowed Adds trailing blank spaces to pad width § Example declaration: student_gender CHAR(1) 23

Character Data Types § NCHAR § Supports 16 -digit binary character codes § Used for alternate alphabets 24

Number Data Type § NUMBER § stores values between 10 -130 and 10126 § General declaration format: variable_name NUMBER(precision, scale) 25

NUMBER Data Types § Number type (integer, fixed point, floating point) specified by precision and scale § Precision: total number of digits on either side of the decimal point § Scale: number of digits to right of decimal point 26

Integer Numbers § Whole number with no digits to right of decimal point § Precision is maximum width § Scale is omitted § Sample declaration: s_age NUMBER (2) 27

Fixed Point Numbers § Contain a specific number of decimal places § Precision is maximum width § Scale is number of decimal places § Sample declaration: item_price NUMBER(5, 2) 28

Floating Point Numbers § Contain a variable number of decimal places § Precision and scale are omitted § Sample declaration: s_GPA NUMBER 29

Date Type § DATE § Stores dates from 1/1/4712 BC to 12/31/4712 AD § Stores both a date and time component § Default date format: DD-MON-YY HH: MI: SS AM § example: 05 -JUN-03 12: 00 AM § Sample declaration: s_dob DATE 30

Specifying Date and Time Values § If no time value is given when a new date is inserted, default value is 12: 00 AM § If no date value is given when a new time is inserted, default date is first day of current month 31

Large Object (LOB) Data Types n Binary Large Object (BLOB) n n Character Large Object (CLOB) n n Stores up to 4 GB of character data BFILE n n Stores up to 4 GB of binary data Stores a reference to a binary file maintained in the operating system NCLOB n Character LOB that supports 16 -bit character code 32

Declaring LOB Data Fields n Item size is not specified Examples: item_image BLOB item_image BFILE n 33

Creating a Database Table § Syntax: CREATE TABLE table_name ( fieldname 1 datatype, fieldname 2 datatype, …); § Example: CREATE TABLE my_students ( s_id NUMBER(6), s_name VARCHAR 2(30), s_dob DATE, s_class CHAR(2)); 34

Constraints n n Rules that restrict the values that can be inserted into a field Types of constraints n n Integrity: define primary and foreign keys Value: specify values or ranges of values that can be inserted 35

Constraint Levels n Table constraint n n n Restricts the value of a field with respect to all other table records Example: primary key value must be unique for each record Column constraint n n Restricts values in a specific column Example: values in an S_GENDER field must be ‘M’ or ‘F’ 36

Constraint Names § Internal name used by DBMS to identify the constraint § Each constraint name in a user schema must be unique § If you do not name a constraint, the system will automatically generate an unintuitive name 37

Constraint Names § Constraint naming convention: tablename_fieldname_constraint. ID § Constraint ID values: § § § Primary key: pk Foreign key: fk Check condition: cc Not NULL: nn Unique: uk § Example constraint name: my_students_s_id_pk 38

Primary Key Constraints § Table-level § Defining a primary key: CONSTRAINT constraint_name PRIMARY KEY § Example: s_id NUMBER(6) CONSTRAINT student_s_id_pk PRIMARY KEY 39

Primary Key Constraints § Can be defined when field is declared 40

Primary Key Constraints § Can also be defined after all table field definitions are completed 41

Composite Primary Keys § Syntax: CONSTRAINT constraint_name PRIMARY KEY (field 1, field 2) § Must be defined after fields that compose key are defined 42

Foreign Key Constraints § 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) 43

Foreign Key Constraints § Can be defined when field is declared 44

Foreign Key Constraints § Can also be defined after all table field definitions are completed 45

Value Constraints § Column-level § Restricts data values that can be inserted in a field § In general, avoid value constraints because they make the database very inflexible 46

Types of Value Constraints § Check condition: restricts to specific values § Example: 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 § Example: CONSTRAINT my_students_s_dob_nn NOT NULL 47

Types of Value Constraints § Default: specifies a default value that is inserted automatically § Example: s_state CHAR(2) DEFAULT ‘WI’ § Unique § Table constraint § Specifies that a non-primary key field must have a unique value CONSTRAINT consultant_c_email_uk UNIQUE (c_email) 48

SQL*Plus § Oracle SQL command line utility for issuing SQL commands § Starting SQL*Plus 49

Using SQL*Plus § All commands must be terminated with a semicolon § Use a text editor and copy and paste commands § Character data is case sensitive and must be in single quotes ‘M’ ‘Sarah’ 50

Exiting SQL*Plus § Type exit at SQL> prompt or § Click Close button on SQL*Plus window 51

Oracle Help Resources § Ora. hlp file § Oracle Technology Network (OTN) § http: //otn. oracle. com 52

Viewing Table Information § Viewing a table’s structure DESCRIBE table_name; 53

Oracle Data Dictionary n Contains tables that describe the database structure n n Is automatically updated as users create and modify tables n n Is in the SYSTEM user schema Cannot be updated directly Contains views that allow users to retrieve information about the database structure 54

Data Dictionary Views n Views present data in different formats depending on the privileges of the user n n n USER: shows all objects belonging to the current user ALL: shows all objects belonging to the current user, as well as objects current user has privileges to manipulate DBA: allows users with DBA privileges to view objects of all database users 55

Querying the Data Dictionary Views n Syntax: SELECT field 1, field 2, … FROM privilege_viewname; 56

Summary of Oracle Data Dictionary Views OBJECTS All database objects TABLES Database tables INDEXES Table indexes created to improve query performance VIEWS Database views SEQUENCES Sequences created to automatically generate surrogate key values USERS Database users CONSTRAINTS Table constraints CONS_CONSTRAINTS Table columns that have constraints IND_COLUMNS Indexed columns TAB_COLUMNS All table columns 57

Modifying Tables § Unrestricted actions § § § Renaming tables Adding new columns Increasing column sizes Dropping columns Dropping constraints 58

Modifying Tables § Restricted actions § Dropping tables § Only allowed if table does not contain any fields that are referenced as foreign keys, or if foreign key constraints are dropped § Changing a column’s data specification § Only allowed if existing data is compatible with new data specification § Decreasing column sizes § Only allowed if column does not contain any data § Adding constraints § Only allowed if existing data meets requirements of new constraint 59

Altering Tables n Adding a new field: ALTER TABLE tablename ADD (fieldname field_specification); 60

Altering Tables n Modifying an existing field: ALTER TABLE tablename MODIFY (fieldname new_field_specification); 61

Altering Tables n Deleting an existing field: ALTER TABLE tablename DROP COLUMN fieldname; 62

Deleting Tables n Syntax to delete table if no table fields are referenced as foreign keys: DROP TABLE tablename; § Syntax to delete table and constraints if table contains fields that are referenced as foreign keys: DROP TABLE tablename CASCADE CONSTRAINTS; 63