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Database Systems

Database Systems. Creating and Modifying Database Objects. Database Objects. An Oracle database consists of multiple user accounts Each user account owns database objects Tables Views Stored programs Etc. Database Queries. Query: command to perform operation on database object

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Database Systems

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  1. Database Systems Creating and Modifying Database Objects

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

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

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

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

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

  7. User Accounts • Each Oracle database user has a user schema • 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

  8. Types of Database Privileges • System Privileges • Control the operations that the user can perform within the database • 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

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

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

  11. Example Oracle System Privileges

  12. Granting System Privileges • Done by DBA • Syntax: GRANT privilege1, privilege2, … TO username;

  13. Database Roles • 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

  14. Creating Roles • Syntax: CREATE ROLE role_name;

  15. Assigning Privileges to a Role • Syntax: GRANT privilege1, privilege2, … TO role_name;

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

  17. Revoking System Privileges • Syntax: REVOKE privilege1, privilege2, … FROM username;

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

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

  20. 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

  21. 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

  22. Oracle Character Data Types • VARCHAR2 • Variable-length character strings • Maximum of 4,000 characters • Must specify maximum width allowed • No trailing blank spaces are added • Example declaration: student_name VARCHAR2(30)

  23. 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)

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

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

  26. 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

  27. 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)

  28. 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)

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

  30. Date 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 12:00:00 AM • Sample declaration: s_dob DATE

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

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

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

  34. Creating a Database Table • Syntax: CREATE TABLE table_name ( fieldname1 datatype, fieldname2 datatype, …); • Example: CREATE TABLE my_students ( s_id NUMBER(6), s_name VARCHAR2(30), s_dob DATE, s_class CHAR(2));

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

  36. Constraint Levels • Table constraint • 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 • Restricts values in a specific column • Example: values in an S_GENDER field must be ‘M’ or ‘F’

  37. 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

  38. Constraint Names • Constraint naming convention: tablename_fieldname_constraintID • 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

  39. 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

  40. Primary Key Constraints • Can be defined when field is declared

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

  42. Composite Primary Keys • Syntax: CONSTRAINT constraint_name PRIMARY KEY (field1, field2) • Must be defined after fields that compose key are defined

  43. 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)

  44. Foreign Key Constraints • Can be defined when field is declared

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

  46. 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

  47. 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

  48. 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)

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

  50. 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’

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