Creating Tables and Primary Keys

4.2. Creating Tables and Primary Keys

The schema in this section is referred to throughout the design chapters of this guide. Let's assume you are designing a flight reservation system. At its simplest, the application requires database tables for the flights, the customers, and the reservations. Example 4.1, 「DDL Example of a Reservation Schema」 shows how the schema looks as defined in standard SQL DDL. For the VoltDB-specific details for creating tables, see CREATE TABLE. When defining the data types for table columns, refer to Table A.1, 「Supported SQL Datatypes」.

Example 4.1. DDL Example of a Reservation Schema

CREATE TABLE Flight (
   FlightID INTEGER UNIQUE NOT NULL,
   DepartTime TIMESTAMP NOT NULL,
   Origin VARCHAR(3) NOT NULL,
   Destination VARCHAR(3) NOT NULL,
   NumberOfSeats INTEGER NOT NULL,
   PRIMARY KEY(FlightID)
);
 
CREATE TABLE Reservation (
   ReserveID INTEGER NOT NULL,
   FlightID INTEGER NOT NULL,
   CustomerID INTEGER NOT NULL,
   Seat VARCHAR(5) DEFAULT NULL,
   Confirmed TINYINT DEFAULT '0'
);
 
CREATE TABLE Customer (
   CustomerID INTEGER UNIQUE NOT NULL,
   FirstName VARCHAR(15),
   LastName VARCHAR (15),
   PRIMARY KEY(CustomerID)
);

To satisfy entity integrity you can specify a table's primary key by providing the usual PRIMARY KEY constraint on one or more of the table’s columns. To create a simple key, apply the PRIMARY KEY constraint to one of the table's existing columns whose values are unique and not null, as shown in Example 4.1, 「DDL Example of a Reservation Schema」.

To create a composite primary key from a combination of columns in a table, apply the PRIMARY KEY constraint to multiple columns with typical DDL such as the following:

$ sqlcmd
1> CREATE TABLE Customer (
2>   FirstName VARCHAR(15),
3>   LastName VARCHAR (15),
4>   CONSTRAINT pkey PRIMARY KEY (FirstName, LastName)5> );