You were so close dude, you just needed to set the usage limit (disc_usage_limit).
Here’s the revised code.
INSERT INTO `discounts` VALUES (1, 0, 8, 0, 0, 0, 0, 0, 0, 'test1', 'test discount code', 0, 0, 0.00, 1.00, 1, 1, 0, 0, '', '', '', 99, '2012-9-19 12:54:41', '2012-9-29 00:00:00', 1, 1);
The usage limit defines how many times the discount can be used, when set to 0, the cart thinks all the discount codes have been used up.
I understand looking at the discount tables is a little daunting with so many columns and options.
To help out in future, I would suggest you create a separate installation of the flexi cart demo so that you can do stuff like build discounts via the provided demo and see what kind of output it does.
If you want/need to create discounts via your site, copy the code from the discount builder in the demo.