SQL Database Structure

The SQL database structure consists of one or more tables. Each table is contained in a file. Tables are defined by rows and columns.

Column 1	Column 2	Column 3	Column 4
Row 1

• row- record - Information about a specific object such as a person.
• column -field - category of information
• key - A unique value in a table that is used to identify that particular object/

SQL Create Command

This command is used to create a table. The syntax of this command is:

create table tablename

(column1name datatype [constraint],

column2name datatype [constraint], 

column3name datatype [constraint]);

Keywords specifying Items that may be created

• table

Data Types

• char(size) - Fixed length string of characters of the set size. The size of the string is limited to 255 characters.
• date
• number(maxsize) - Number with a maximum number of digits specified by "maxsize".
• number(maxdigits,maxright) - A decimal number with a manimum number of "maxdigits" with "a maximum number of digits to the right of the decimal, "maxright".
• varchar(maxsize) - A character string with variable lingth limited to "maxsize".

Constraints

Constraints are rules for the column.. Possible values include:

• not null - The column values must have a value and cannot be null.
• primary key - Each record is uniquely identified by this column.
• unique - No two values may be the same in the column

Example

create table citylist

(name varchar(20),

state varchar(20),

population number(8),

zipcode number(5) unique);