DB2 Introduction

DB2 is the database that most COBOL programs on the mainframe talk to. This module introduces the key DB2 concepts you need first: what a database management system is, how the relational model stores data in tables, what normalization does, and how SQL talks to DB2.

What you will learn in this module

• What a Database Management System (DBMS) is and why it exists
• The advantages of a DBMS over plain files
• How the relational database model organizes data into tables, rows and columns
• How tables are related to each other through primary keys and foreign keys
• What normalization is, and the first three normal forms (1NF, 2NF, 3NF)
• The three families of SQL in DB2: DDL, DML and DCL
• The main DB2 objects: databases, tablespaces, tables, indexes, views, synonyms and aliases

Database Management System (DBMS)

• A DBMS stores information in electronic form.
• It makes information available for sharing by users or programs.
• It provides facilities to developers to define data to the system.
• It provides facilities to users or programs to retrieve or change the data.
• It provides facilities for security and recovery, so data is protected and can be restored after a failure.
• It maintains information consistency throughout the database, so every user sees the same correct data.

Why this module matters for a COBOL programmer

• Most COBOL batch programs on the mainframe read from and write to DB2 tables instead of flat files.
• You will embed SQL inside COBOL programs (between EXEC SQL and END-EXEC) to fetch and update rows.
• Understanding tables, keys and normalization helps you write correct SQL and debug wrong results.
• SQL statements return a status code (SQLCODE) after every execution; knowing the objects involved makes those codes easier to read.

Your first look at SQL

• SQL (Structured Query Language) is the language used to talk to a DB2 database.
• Here is a simple SQL statement that reads rows from a table:-
  
  SELECT EMPNO, LNAME, FNAME FROM EMPLOYEE WHERE DEPTNO = 'B12'
• This SELECT asks DB2 for the employee number, last name and first name of every employee in department B12.
• All code examples in this module are plain SQL that you can run in any DB2 SQL tool.