Database Reference
In-Depth Information
Note
Table Names What makes a table name unique is actually a combination of several
things, including the database name and table name. This means that while you cannot
use the same table name twice in the same database, you definitely can reuse table
names in different databases.
Tables have characteristics and properties that define how data is stored in
them. These include information about what data may be stored, how it is
broken up, how individual pieces of information are named, and much more.
This set of information that describes a table is known as a
schema
, and schema
are used to describe specific tables within a database, as well as entire databases
(and the relationship between tables in them, if any).
New Term
Schema Information about database and table layout and properties.
Note
Schema or Database? Occasionally
schema
is used as a synonym for database (and
schemata
as a synonym for databases). While unfortunate, it is usually clear from the
context which meaning of schema is intended. In this topic, schema will refer to the
definition given previously.
Tables are made up of columns. A column contains a particular piece of infor-
mation within a table.
New Term
Column A single field in a table. All tables are made up of one or more columns.
The best way to understand this is to envision database tables as grids, some-
what like spreadsheets. Each column in the grid contains a particular piece
of information. In a customer table, for example, one column contains the
customer number, another contains the customer name, and the address, city,
state, and Zip Code are all stored in their own columns.
Tip
Breaking Up Data It is important to break data into multiple columns correctly. For
example, city, state, and Zip Code should always be separate columns. By breaking
these out, it becomes possible to sort or filter data by specific columns (for example,
to find all customers in a particular state or in a particular city). If city and state are
combined into one column, it would be difficult to sort or filter by state.
