Define Tables and Fields

2.2 Define Tables and Fields
A SQL Server database doesn't do much good unless you have tables in it. This tutorial
not only gives you information on how to create tables and fields, but also teaches you
how to name them and what to look out for when creating them. Databases by themselves
don't do much for you, but you need to be able to store data in them at the very least. To
do this, you need to be able to create tables, which are made up of fields. How do you go
about defining tables and fields in VS .NET?
Technique
Using the Server Explorer and accessing the Table designer, you are going to create a
table called tblCustomers in the database that you created in the previous How-To. You
will then add columns to the database that will store various pieces of information having
to do with individual customers.
Last, you will create another table called tblPhones and also create the necessary columns
that will contain information about phone information for your customers.
Steps
After Visual Studio .NET is opened, expand the Server Explorer and locate your new
database called Chapter2, created in How-To 2.1. Click on the plus sign by the database
names so that the database object categories are listed.
1. Right-click on the Tables node under the Chapter2 database and choose New
Table. You will then be presented with the Table Designer. Now you are ready to
add the columns.
2. To add a column, you need to set four immediate properties:
o
Column Name. This is the name of the column. Don't use spaces or special
characters, but do use proper case, and make sure that the name you give
the column makes sense for what it contains. For instance, if the column is
for the last name of a customer, put LastName for the Name property of the
column.
o
Data Type. Depending on the type of data that will be entered into the
column, this will be one of the many valid data types for SQL Server,

shown here in Table 2.1.
Table 2.1. SQL Server Data Types
Data Type Description
bigint Integer (whole number) data from -2
63
(-
9,223,372,036,854,775,808) through 2
63
\up6 - 1\up6
(9,223,372,036,854,775,807).
int Integer (whole number) data from -2^31 (-
2,147,483,648) through 2
31
- 1 (2,147,483,647).
smallint Integer data from 2
15
(-32,768) through 2
15
- 1 (32,767).
tinyint Integer data from 0 through 255.
bit Integer data with either a 1 or 0 value.
decimal Fixed precision and scale numeric data from -10
38
+ 1
through 10
38
- 1.
numeric Functionally equivalent to decimal.
money Monetary data values from -2
63

(-
922,337,203,685,477.5808) through 2
63
- 1
(+922,337,203,685,477.5807), with accuracy to a ten-
thousandth of a monetary unit.
smallmoney Monetary data values from -214,748.3648 through
+214,748.3647, with accuracy to a ten-thousandth of a
monetary unit.
float Floating precision number data from -1.79E + 308
through 1.79E + 308.
real Floating precision number data from -3.40E + 38 through
3.40E + 38.
datetime Date and time data from January 1, 1753, through
December 31, 9999, with an accuracy of three-
hundredths of a second, or 3.33 milliseconds.
smalldatetime Date and time data from January 1, 1900, through June 6,
2079, with an accuracy of one minute.
char Fixed-length non-Unicode character data with a
maximum length of 8,000 characters.
varchar Variable-length non-Unicode data with a maximum
length of 8,000 characters.
text Variable-length non-Unicode data with a maximum
length of 2
31
- 1 (2,147,483,647) characters.
nchar Fixed-length Unicode data with a maximum length of
4,000 characters.
nvarchar Variable-length Unicode data with a maximum length of
4,000 characters.

ntext Variable-length Unicode data with a maximum length of
2
30
- 1 (1,073,741,823) characters.
binary Fixed-length binary data with a maximum length of
8,000 bytes.
Varbinary Variable-length binary data with a maximum length of
8,000 bytes.
image Variable-length binary data with a maximum length of
2
31
- 1 (2,147,483,647) bytes.
cursor A reference to a cursor.
sql_variant A data type that stores values of various SQL Server-
supported data types, except text, ntext, timestamp, and
sql_variant.
table A special data type that stores a result set for later
processing.
timestamp A database-wide unique number that is updated every
time a row is updated.
uniqueidentifier A globally unique identifier (GUID).
o
Tip

Unicode is a character-encoding standard that uses 16-bit
code values. This standard is used worldwide to represent
all the characters that are used in modern computing.
Traditional character sets are the previous character-
encoding standards-such as the Windows ANSI character
set-that use 8-bit code values or combinations of 8-bit

values to represent the characters used in a specific
language or geographical region.
It is recommended that you use Unicode data types-nchar,
nvarchar, and ntext-rather than their non-Unicode
counterparts.
Also, use the variant length type data types whenever
possible. Doing so will save disk space and save you from
having to trim your values when you want to display the
data in the fields.
o
Length. This varies depending on which data type you choose. For text data
types, this will be the maximum length you expect to be entered into the
column.
o
Allow Nulls. This specifies whether you will allow null values to be saved
in the record for the column. This means that the user doesn't have to enter
a value at all. This is sometimes a bad idea, such as when you have specific
data that has to be entered, like Social Security Numbers.
For the first few columns in the table, enter the following data. You can see how
the table will look in Figure 2.3.
Figure 2.3. Fields for your first table.

Column Name Data Type Length Allow Nulls
LastName nvarchar 50 Unchecked
FirstName nvarchar 50 Unchecked
Address nvarchar 50 Checked
City nvarchar 50 Checked
State nvarchar 2 Checked
ZipCode nvarchar 9 Checked
BirthDate datetime 8 Checked

MailingList bit 1 Checked
EstimatedSales money 8 Checked
3. Save the table by clicking on the X in the top-right corner of the Table Designer,
and name the table tblCustomers when prompted. After you click the X, you are
asked if you want to save the table. Then you are prompted for the name to save
the table as.
How It Works
By entering the information in the various properties for each column, you are specifying
how you want the data in your database to be treated. Generally, your users won't create
tables; you will create the tables for the users, and they will fill the data into the tables
using your applications.
When the user fills in the data, the application and SQL Server control what type of data
goes into the table, starting with what the data type of the data is and what the allowed
length is. The Allow Nulls property determines whether the user even has to enter data.
Comments
Creating the tables, made up of columns and rows, is the basis for the database's purpose:
storing information. Making sure that you use logical, descriptive names for columns,
along with data types that help control how the data gets entered into the database, is key
to a successful database. Plan out your tables ahead of time, examining each real-world
object, and transfer those properties to the columns that make up the tables that represent
your objects.