Costco Wholesale Corp. reported better than expected sales results for December as online shopping soared. The warehouse chain reported net sales of $19.14 billion for the five-week period ending Jan. 3, up 12.3% from a year earlier. Comparable sales, a closely watched performance metric that looks at sales at warehouse-club locations open for more than a year, rose 10.7%. Excluding the impact from gasoline sales and currency swings, core comparable sales rose 10.9%. Analysts surveyed by Consensus Metrix expected a 10.1% comparable-sales increase, or 11.2% when adjusted for gas sales and cu...