.NET & XML

Reading Data

Angus Hardware, like most retail stores, occasionally offers its customers discounts in the form of coupons. They like to track which customers take advantage of which coupons, both as a marketing tool, and to aid in fraud detection. They’ve decided that the best way to manage this coupon usage data is with a relational database.

Figure 11-1 shows the portion of the coupon database schema I use in this chapter.

Figure 11-1. Coupon database schema

The results of any SQL select statement come in the form of a table of data. Although it may not represent any actual table in the database, it still consists of rows and columns. Take, for example, the following query:

select coupon_code, total_discount, redemption_date 
from coupon_redemptions
where redemption_date >= '11/7/2002' order by customer_id;

This query returns a table of data that looks like Table 11-1.

Table 11-1. Results of SQL select statement

coupon_code	total_discount	redemption_date
117GG	10.00	11/7/2002
167YH	10.00	11/8/2002
987UI	20.00	11/8/2002
...

The coupon_redemption table actually contains other columns, but because I only selected three, the result set only includes those three. In fact, you can see that these results are actually returned in order of a column that is not included in the result set, the customer_id. The result set also does not include all the rows, ...