It's summer, and Walmart and Amazon are celebrating by escalating their e-commerce competition. Amazon on Thursday announced it would hold its second annual Prime Day on July 12. A shopping day for Amazon Prime members worldwide, it is billed as the biggest global Amazon event ever. The company will offer more than 100,000 bargains, with new deals popping up at five minute intervals throughout the day. Last year's Prime Day was a bigger day for sales than the biggest Black Friday ever, up to that point, Amazon pointed out.