LECTURE8: SQL OVERVIEW , ORACLE DATA TYPE , DDL AND CONSTRAINTS Ref. Chapter6 from “Database Systems: A Practical Approach to Design, Implementation and Management.” Thomas Connolly, Carolyn Begg. IS220 : Database Fundamentals Chapter Objectives 2 In this chapter you will learn: The data types supported by the SQL standard. How to define integrity constraints using SQL including: required data; domain constraints; entity integrity; referential integrity; general constraints. How to use the integrity constraints in the CREATE and ALTER TABLE The Process of Database Design 3 Logical Design Conceptual Design (ERD) (Relational Physical Design Model) Create schema Load Data (DDL) (DML) STRUCTURED QUERY LANGUAGE SQL SQL Overview 5 Official pronunciation is ‘S-Q-L‘ or ( see-qual) SQL: Structured Query Language The standard for relational database management systems (RDBMS) such as Oracle Database. All SQL statements are instructions to the database. Easy to learn: Consists of standard English words, case insensitive It is a non-procedural language: you specify what information you require, rather than how to get it. In other words, SQL does not require you to specify the access methods to the data SQL in Oracle 6 • SQL is made up of 4 components: 1. Data Definition Language (DDL) 2. Data Manipulation Language (DML) 3. Data Control Language (DCL) 4. Transaction control statements SQL Components 7 1. The Data Definition Language (DDL) This component of the SQL language is used for defining the database structure and to create and modify tables and other objects in the database. For tables there are three main commands: 1. CREATE TABLE tablename : to create a table in the database 2. DROP TABLE tablename : to remove a table from the database 3. ALTER TABLE tablename : to add or remove columns from a table in the database SQL Components 8 2. The Data Manipulation Language (DML) component of the SQL language is used for retrieving and updating data There are four main commands: 1. SELECT : to select rows of data from a table. 2. INSERT : to insert rows of data into a table. 3. UPDATE : to change rows of data in a table. 4. DELETE : to remove rows of data from a table. SQL Components 9 3. The Data Control Language (DCL) This component of the SQL language is used to create privileges to allow users access to, and manipulation of, the database. There are two main commands: 1. GRANT : to grant a privilege to a user 2. REVOKE : to revoke (remove) a privilege from a user 4. Transaction control statements • COMMIT, ROLLBACK DATA DEFINITION LANGUAGE ( DDL ) Table Creation 10 Data Definition (Creating a table) 11 CREATING A TABLE Syntax: create table table-name ( column-name1 datatype , …….. column-nameN datatype ); Table Name CONDITIONS : can not exceed 30 characters long Must begin with an alphabetic character May contain letters, numbers, $, # and _ Should not be an oracle reserved word Should be descriptive Built-In Oracle Data type Summary 12 Built-in Data type Description Max Size: Oracle 9i/10g VARCHAR2(size 4000 bytes Variable length character string having [BYTE | CHAR]) minimum is 1 maximum length size bytes. You must specify size Fixed length character data of length size 2000 bytes CHAR(size) bytes. This should be used for fixed length Default and minimum size is 1 data. Such as codes A100, B102... byte. NUMBER(p,s) Number having precision p and scale s. The precision The precision p can range from 1 p can range from 1 to 38. to 38. The scale s can range from -84 to127. The scale s can range from -84 to 127. DATE Valid date range from January 1, 4712 BC to from January 1, 4712 BC to December 31, 9999 AD. December 31, 9999 AD. TIMESTAMP[timePre Year, month, and day values of date, as well as Accepted values of csion] hour,minute, and second values of time, fractional_seconds_precision are 0 to 9. (default = 6) NUMBER(p,s) 13 Syntax for specifying numbers Number (precision, scale) Precision is the maximum digits of numbers Scale specifies the position of decimal point. E.g. Number(5) 5 digit integer, ex) 12345 Number(6,2) 6 digit (not including decimal point) decimal number with 2 digits after the decimal point , ex) 1234.56 Can store 1—38 digits precision String 14 To store strings, you can choose from: Char (size) stores fixed-length character strings of up to 2000 characters. Eg. char(10) Use it to store short strings Varchar2 (size) Stores variable-length strings of up to 4000 characters long. Eg. Varchar2(50) Preferred for most string types Must specify the size String values are quoted with single quotes Eg ‘12234’, ‘abcd’, ‘a12’ Date and time 15 Oracle uses the date data type to store both date and time Always uses 7 bytes for date-time data. Oracle date has rich formats, you need to specify it SS second 0-59 MI Minute 0-59 HH Hour 1-12 HH24 Military hour 1-24 DD day of month 1-31 (depends on month) DAY day of the week Sunday-Saturday D day of the week 1-7 MM month number 1-12 MON month abbreviated Jan—Dec Month Month spelled out January-December YY last 2 digits of year eg, 98 YYYY full year value eg, 1998 Date and time 16 Example of date format: ‘dd-mon-yyyy’ 01-dec-2001 ‘dd/mm/yyyy’ 01/12/2001 ‘mm-dd-yy hh:mi:ss’ 12-01-01 12:30:59 Default format: ‘dd-mon-yyyy’ Current date and time: Sysdate Example 17 CREATE TABLE Persons ( P_Id char(5) , LastName varchar2(255), FirstName varchar2(255), Sex char(2), ); 18 Integrity Constraints 19 An integrity constraint defines a business rule for a table column. When enabled, the rule will be enforced by oracle constraints can be defined at either the table level or the column level. If the results of an INSERT or UPDATE statement violate an integrity constraint, the statement will be rolled back. Note : If you don’t give the constraint name, the system will generate a name automatically, but the name is hard for human understanding. Integrity Constraints 20 Constraint clauses can appear in the following statements: 1. CREATE TABLE 2. ALTER TABLE 3. CREATE VIEW 4. ALTER VIEW The types of integrity constraint 21 1. NOT NULL constraint 2. UNIQUE constraint 3. PRIMARY KEY constraint 4. FOREIGN KEY constraint 5. CHECK constraint NOT NULL constraint 22 The NOT NULL constraint enforces a field to always contain a value. This means that you cannot insert a new record, or update a record without adding a value to this field. Defined at column level ONLY Syntax: CREATE TABLE table-name ( column-name1 datatype NOT NULL ); OR CREATE TABLE table-name ( column-name1 datatype CONSTRAINT constraint_name NOT NULL ); Example: NOT NULL 23 CREATE TABLE employees( employee_id NUMBER(6), System last_name VARCHAR2(25) NOT NULL, named salary NUMBER(8,2), commission_pct NUMBER(2,2), User hire_date DATE CONSTRAINT emp_hire_date NOT NULL ); named SQL NULL 24 If a column in a table is optional, we can insert a new record or update an existing record without adding a value to this column. This means that the field will be saved with a NULL value. NULL values are treated differently from other values. NULL is used as a placeholder for unknown or inapplicable values. Note: It is not possible to compare NULL and 0; they are not equivalent. It is not possible to test for NULL values with comparison operators, such as =, <, or <>. We will have to use the IS NULL and IS NOT NULL operators instead. UNIQUE constraint 25 The UNIQUE constraint prohibits multiple rows from having the same value in the same column or combination of columns but allows some values to be null. Defined at either the table level or the column level Unique columns are not automatically NOT NULL Syntax: 1 - column level CREATE TABLE table-name ( column-name1 datatype UNIQUE ); 2 - table level CREATE TABLE table-name ( ……. [CONSTRAINT constraint-name] UNIQUE (Columns_list)) ; The UNIQUE Constraint 26 UNIQUE constraint EMPLOYEES Allowed Not allowed: already exists Example: UNIQUE 27 The following SQL creates a UNIQUE constraint on the "P_Id" column when the "Persons" table is created: CREATE TABLE Persons Column level ( P_Id char(5) NOT NULL UNIQUE, LastName varchar2(255) NOT NULL, FirstName varchar2(255), Address varchar2(255), Telephone varchar2(10), Table level City varchar2(255), UNIQUE (LastName, FirstName), CONSTRAINT tel_unique UNIQUE (telephone) ); Primary Key Constraint 28 A primary key constraint combines a NOT NULL constraint and a UNIQUE constraint in a single declaration. That is, it prohibits multiple rows from having the same value in the same column or combination of columns and prohibits values from being null. A PRIMARY KEY constraint automatically has a UNIQUE constraint defined on it. Defined at either the table level or the column level Note that you can have many UNIQUE constraints per table, but only one PRIMARY KEY constraint per table. Primary Key Constraint 29 1- Table level CREATE TABLE table-name ( column-name1 datatype, …….. column-nameN datatype, [CONSTRAINT constraint-name] PRIMARY KEY (columns-name)); OR 2- Column level CREATE TABLE table-name ( column-name1 datatype PRIMARY KEY, …….. column-nameN datatype); Example: Primary Key 30 Column Level CREATE TABLE Department ( Column level Dept_no char(4) PRIMARY KEY, Dept_name varchar2(25)); OR Table Level CREATE TABLE Department ( dept_no char(4), Table level Dept_name varchar2(25), CONSTRAINT dept_PK PRIMARY KEY (dept_no)); FOREIGN KEYS constraint 31 foreign key constraint requires values in one table to match values in another table. Syntax: CREATE TABLE table-name ( column-name1 datatype, …… …… [CONSTRAINT constraint-name] FOREIGN KEY (Column_name) REFERENCES referenced_table (column_in_referenced_table) ); Example: Foreign Keys 32 Create table Employee( EMPLOYEE_ID NUMBER(3) PRIMARY KEY, LAST_NAME varchar2(20), DEPARTMENT_ID NUMBER(3), CONSTRAINT EMP_Fk FOREIGN KEY (DEPARTMENT_ID) REFERENCES Department (DEPARTMENT_ID)); The FOREIGN KEY Constraint 33 Department PRIMARY KEY 90 Employee FOREIGN KEY Not allowed INSERT INTO (9 does not exist) Allowed Referential integrity constraints 34 When you delete or update a value of the columns referenced by other tables, the referential integrity constraints may be violated.