MYSQL keywords:
SQL_CALC_FOUND_ROWS
to check the manual and found this keyword is used in the query result of statistical filtering conditions when the total number of (not restricted by Limit)
For example:

SELECT SQL_CALC_FOUND_ROWS tid FROM cdb_threads WHERE fid=14 LIMIT 1,10;

Let’s say there are 1,000 that satisfy our condition, and we return 10.

for immediate use

SELECT found_rows() AS rowcount;

Return rowcount = 1000;
this saved a SELECT count (*) AS the rowcount repeat query, can save considerable time.

From: http://ginew.blog.163.com/