Turning the result around

In many cases you don't want your the result from your SQL statement in just a plain listing, but organized in columns, or whith data grouped on status, period or whatever. This can often be accomplished with a combination of the IF function and SUM or another group function.

For example get your sales per customer grouped by period:
SELECT customer_no AS CUSTNO, cust_name AS CUSTNAME,
sum(if(period = '200701',amount,0) as Jan_Amount,
sum(if(period = '200702',amount,0) as Jan_Amount
FROM otd.salestrans_hist s
WHERE period IN ('200701','200702')
GROUP BY customer_no, cust_name

Or number of open and closed records in each class:
SELECT class, sum(if(status='Open',1,0)) as open,
sum(if(status='Closed',1,0)) as closed
FROM table_name
GROUP BY class

In the examples I have used the MySQL IF function. You could also use CASE, which is SQL standard.