Run Oracle. Click "Connect to Database" and select the database you wish to edit.
Open the SQL query window. Type "CREATE TABLE" if you wish to add a new table with a constraint or "ALTER TABLE" to add a constraint to an existing table. Enter the name of the table after the command.
Define the fields within the table if you are creating a new table. Supply the name of the field, the type of value to accept and whether the field can be empty. For example, "CREATE TABLE table ( field_id numeric(10) not null, field_name varchar2(50) not null, field_description varchar2(255)" would create a table with three columns -- field_id, field_name and field_description.
Add the constraint. Type "add CONSTRAINT constraint_name OPERATION (column#)" without the quotation marks after the "ALTER TABLE" command if you are constraining an existing table. Type "CONSTRAINT constraint_name OPERATION (column#)" without the quotation marks after defining the fields within the table if you are creating a new table.
Replace "constraint_name" with the name you wish to give the constraint. Change "OPERATION" to the command by which you wish to constrain the table, such as the command "UNIQUE()" that checks for duplicate entries in the selected fields. For example "CONSTRAINT field_unique UNIQUE (field_id, field_name)" checks the field_id and field_name of an entry against existing entries to make sure it is not a duplicate before adding it to the table.
Close any open-ended commands so all parenthesis pair up. Finish the statement with a delimiter, usually a semicolon. For example "CREATE TABLE table ( field_id numeric(10), CONSTRAINT field_unique UNIQUE(field_id));"
Click "Run" to commit the query to the database.