SQL: Structured Query Language - Oracle 10g Database Administration Concepts and Implementation Made Simple - page 12

for MS SQL server in less than an hour. There is one SQL
standard defined by ANSI (American National Standard
Institute) and is called ANSI SQL. Nearly all RDBMS database
manufacture incorporates this ANSI SQL and then builds a layer
of some new stuff on top of it to provide added functionality in
the language. The SQL that we will be learning in this topic will
be more precisely Oracle SQL.
Concept of arranging the data in the form of table is very simple.
We have been doing it on the papers for years and the concept is
still the same. There are two terms that we will be using a lot.
One is called “Record(s)” or “Row(s)” and other one is called
“Field(s)” or “Column(s)”. Like shown in the figure below, there
are 5 records in the table and 3 fields. Each field in Oracle table
has been assigned a “Data type”. While creating a table if you
have assigned Last Name field “character” data type, you should
not insert date or numeric value in it. We will learn this stuff in
great detail when we learn about CREATE TABLE statement.
There is one more thing that we can do with fields, we can assign
constraints on them e.g. If you assign UNIQUE constraint on any
column then you would not be able to insert any value in it
which is already there. Constraints help in maintaining the data
integrity of the system.
Figure 2-2: Table Showing Records/Rows And Fields/Columns