The shopping wars are heating up this July as Dollar General and Walmart offer discounts ahead of Amazon's Prime Day

Amazon's longest-ever Prime Day has competition from even longer sales from other retailers this year.

Brendan McDermid/Reuters

• Amazon Prime Day has competition from a list of other retailers, from Walmart to Dollar General.
• Some rivals are offering longer sales or starting their discounts ahead of Prime Day.
• It's a chance for other retailers to challenge Amazon's dominance, one analyst said.

What used to be one of the sleepiest times of year for retailers...