Amazon’s self-created sales holiday on July 12 — Prime Day — set records for the two-year old event, and offered cues to longer-term shifts in retailing trends. Amazon’s success with Prime Day is a testament to the stickiness of its customers, whose growing numbers reveal the huge distance rival Walmart has to cover, according to experts. Prime Day sales also came as a windfall for retailers. The only other big retail event this time of the year is the back-to-school shopping season during July and August. Amazon, meanwhile, is shifting strategies, pushing the “convenience” it offers as a shopping destination instead of its earlier, low-price positioning, analysts note. On Prime Day, Amazon saw its online orders increase by more than 60% worldwide and 50% in the U.S., the company said in a press release . That day, it sold globally more than 90,000 TVs, more than two million toys and more than a million pairs of shoes, among other products.…