By Neha Alawadhi (Reuters) - Data analytics firm Teradata Corp cut its full-year earnings forecast by about 10 percent after preliminary third-quarter results missed estimates on the back of sliding revenue, sending its shares down 12 percent in extended trading. The company has been struggling to compete against cheaper products from bigger rivals such as Oracle Corp, FBN Securities analyst Shebly Seyrafi said, even as demand soars for tools to analyze vast amounts of data stored in real time. Teradata, which counts Cisco Systems Inc, ebay Inc and Verizon Communications Inc among its customers, estimated adjusted earnings of 69-70 cents per share on revenue of about $665 million for the quarter ended September 30. Analysts on average were expecting earnings of 81 cents on revenue of $699 million, according to Thomson Reuters I/B/E/S. The company said revenue fell about 21 percent in its Asia, Pacific, and Japan markets and about 19 percent in its Middle East and Africa markets. Full-year adjusted earnings forecasts were revised down from the low end of the $3.05 to $3.20 per share range to between $2.70 and $2.80 per share. The company's third-quarter results are due to be released on October 31. Teradata has missed profit estimates only once in the last eight quarters. Revenue from the international business, which accounts for about 40 percent of the company's sales, has fallen for the second successive quarter. The company's shares closed at $52.58 on the New York Stock Exchange on Monday. They fell to $46.11 in extended trading. Out of the 27 analysts covering Teradata, 18 have either a "buy" or a "strong buy" rating on the stock and 8 have a "hold" rating, according to StarMine. (Reporting by Neha Alawadhi and Lehar Maan in Bangalore; Editing by Stephen Coates)