mysql里一条包含分组，排序，取前n条的sql语句如下
select create_time,price,sum(num) num from t1 WHERE sid="a" AND rid="b" GROUP BY price ORDER BY price ASC,create_time ASC LIMIT 10在KDB+里的写法如下
select [10] from `price xasc {select num:sum num by price from t1 where sid=(x 0),rid=(x 1)}(`$"a";`$"b")[10]对应的是LIMIT 10
`price xasc 对应的是 ORDER BY price ASC
num:sum num对应的是sum(num) num
by price 对应的是ORDER BY ASC
