Creating Tables - IV

The create table statement is used to create a new table. Here is the format of a simple create table statement:

create table "tablename"
("column1" "data type",
 "column2" "data type",
 "column3" "data type");

Format of create table if you were to use optional constraints:

create table "tablename"
("column1" "data type" 
         [constraint],
 "column2" "data type" 
         [constraint],
 "column3" "data type" 
        [constraint]);
 [ ] = optional

Note: You may have as many columns as you'd like, and the constraints are optional.

Example:

create table employee
(first varchar(15),
 last varchar(20),
 age number(3),
 address varchar(30),
 city varchar(20),
 state varchar(20));

To create a new table, enter the keywords create table followed by the table name, followed by an open parenthesis, followed by the first column name, followed by the data type for that column, followed by any optional constraints, and followed by a closing parenthesis. It is important to make sure you use an open parenthesis before the beginning table, and a closing parenthesis after the end of the last column definition. Make sure you seperate each column definition with a comma. All SQL statements should end with a ";".

The table and column names must start with a letter and can be followed by letters, numbers, or underscores - not to exceed a total of 30 characters in length. Do not use any SQL reserved keywords as names for tables or column names (such as "select", "create", "insert", etc).

Data types specify what the type of data can be for that particular column. If a column called "Last_Name", is to be used to hold names, then that particular column should have a "varchar" (variable-length character) data type.

Here are the most common Data types:

char(size)	Fixed-length character string. Size is specified in parenthesis. Max 255 bytes.
varchar(size)	Variable-length character string. Max size is specified in parenthesis.
number(size)	Number value with a max number of column digits specified in parenthesis.
date	Date value
number(size,d)	Number value with a maximum number of digits of "size" total, with a maximum number of "d" digits to the right of the decimal.

What are constraints? When tables are created, it is common for one or more columns to have constraints associated with them. A constraint is basically a rule associated with a column that the data entered into that column must follow. For example, a "unique" constraint specifies that no two records can have the same value in a particular column. They must all be unique. The other two most popular constraints are "not null" which specifies that a column can't be left blank, and "primary key". A "primary key" constraint defines a unique identification of each record (or row) in a table. All of these and more will be covered in the future Advanced release of this Tutorial. Constraints can be entered in this SQL interpreter, however, they are not supported in this Intro to SQL tutorial & interpreter. They will be covered and supported in the future release of the Advanced SQL tutorial - that is, if "response" is good.

It's now time for you to design and create your own table. You will use this table throughout the rest of the tutorial. If you decide to change or redesign the table, you can either drop it and recreate it or you can create a completely different one. The SQL statement drop will be covered later.