sort column only的意思|示意

Note that if several counting functions or tests operate on the same column, then the sort and count operations only need to be done once.

注意，如果多个计数函数或测试在同一列上运行，那么排序与计数操作仅需做一次。

Here DB2 can match on only one column, and since LASTNAME is random, DB2 must do a data sort to bring our rows back in LASTNAME, EMPNO order.

这里DB 2仅可在一列上匹配，并且因为LASTNAME是随机的，DB 2必须执行数据排序来以LASTNAME、EMPNO顺序返回我们的行。