Data Base week5_1

22/02/2010

 
 

SQL (Structured Query Language)
A standardized non-procedural language used to create, manipulate and manage a database; consists of:

• Data Definition Language (DDL)
  
  • Commands that create, alter and drop tables
    
• Data Manipulation Language (DML)
  
  • Commands that maintain and query tables
    
• Data Control Language (DCL)
  
  • Commands that administer privileges and commit data
    

 
 

Constrains (not must but for used by human being.)

• Constraints enforce rules at the table level.
  
• Constraints prevent the deletion of a table if there are dependencies.
  
• The following constraint types are valid in SQL:
  
  • NOT NULL
    
  • UNIQUE
    
  • PRIMARY KEY
    
  • FOREIGN KEY
    
  • CHECK