SQL

1. SQL has become the standard relational database language. It has several parts:
   • Data definition language (DDL) - provides commands to
     • Define relation schemes.
     • Delete relations.

     • Create indices.
     • Modify schemes.

   • Interactive data manipulation language (DML) - a query language based on both relational algebra and tuple relational calculus, plus commands to insert, delete and modify tuples.

   • Embedded data manipulation language - for use within programming languages like C, PL/1, Cobol, Pascal, etc.
   • View Definition - commands for defining views

   • Authorization - specifying access rights to relations and views.

   • Integrity - a limited form of integrity checking.
   • Transaction control - specifying beginning and end of transactions.
   We will only look at basic DDL, the DML and views. Integrity features will be covered in Chapter 5.

• Basic Structure
• Set Operations & Duplicate Tuples
  • Set Operations
• Predicates & Joins
• Set Membership
• Tuple Variables
• Set Comparison
• Testing for Empty Relations
• Ordering the Display of Tuples
• Aggregate Functions
• The Power of SQL
• Modifying the Database
  • Deletion
  • Insertion
  • Updates
• Null Values
• Views
• Data Definition