`1. A database management system provides a set of integrated data management services or tools which are
used to maintain and manage logical groupings of data or information.
In this branch of mathematics, a table is called a relation.
2. Codd's original theory was based on 12 principles.
(1)The first is that all data in an RDBMS is stored in tables.
(2)Another principle is that you need a language to retrieve or manipulate data in these tables. This language is
known as SQL and is part of the relational theory.
3. A table consists of columns and rows. Columns are the attributes of the entity. They are the same for every
particular instance of the entity.
Every particular instance of the entity is a row. Rows are not usually stored in any particular order.
There is only one value at every row and column position in a table. This means that all data values are atomic.
4. There must be some way to identify uniquely just one instance or row of a table in order to manipulate the data in
it. The unique key will allow you to do just that.
5. There are two terms you may hear to describe SQL. The first is non-navigational. This means that you only need
to tell DB2, through SQL, what data you want. You do not need to specify how DB2 is to get that data. By using the
optimizer, DB2 determines the best access path. For example, it decides whether to use an index to retrieve data.
SQL is also a non-procedural language. A procedural language is a programming language such as C or COBOL.
SQL is not a programming language. It does not do looping or go through extensive if-then-else steps one record at a
time. SQL handles a set of records in a table and can be embedded into a programming language to take advantage
of the capacity of the language to carry out procedural logic on that data.
6. Data Manipulation Language (DML) allows you to retrieve and manipulate data. SELECT is your basic read
statement. Both SELECT and UPDATE work at the column level. INSERT and DELETE function at the row level.
Data Definition Language (DDL) allows you to CREATE and maintain the physical data structures or objects in your
database. You CREATE a table or index. The ALTER statement allows you to add a column to the end of a table. If
you no longer need an object, you can simply DROP that object.
Control Language provides the control statements that govern data security. You must be authorized to use various
objects in DB2. You need to be granted the ability to SELECT, UPDATE, INSERT, or DELETE against a table and to
CREATE a table. If you no longer need these privileges, they can be revoked.
