PostgreSQL, Second Edition

Arrays

One of the unique features of PostgreSQL is the fact that you can define a column to be an array. Most commercial database systems require that a single column within a given row can hold no more than one value. With PostgreSQL, you aren't bound by that rule—you can create columns that store multiple values (of the same data type).

The customers table defined in Chapter 1 contained a single balance column. What change would you have to make to the database if you wanted to store a month-by-month balance for each customer, going back at most 12 months? One alternative would be to create a separate table to store monthly balances. The primary key of the cust_balance might be composed of the customer_id and the month number (either 0-11 or ...