Test MySQL date calculations

This is a way to test certain SQL queries involving dates. Say a query is supposed to select "Last Saturday", regardless of the date on which it runs:

SELECT DATE_SUB(CURDATE(), INTERVAL WEEKDAY(DATE_SUB(CURDATE(), INTERVAL 5 DAY)) DAY) AS 'Last Saturday';

How do you know if it really works on all days? This command will iterate through all the days in the month, and run the query with each date to see what it gets:

for day in $(seq 1 30)

do

    echo Nov $day, $(mysql -u sdkain -h db21 lf_wh -e"SELECT DATE_SUB('2010-11-$day', INTERVAL WEEKDAY(DATE_SUB('2010-11-$day', INTERVAL 6 DAY)) DAY) AS 'Last Sunday'")

done

Remember to test for when the year changes, and on leap years.