The return value of any function is the result of the last expression in that clause (in our examples there is only one line).
任何函数的返回值都是子句(在我们的示例中只有一行)中最后一个表达式的结果。
2
If all the columns in the clause appear in the required sequence with a single index, the database server USES the index to read the rows in the ordered sequence, thus avoiding a sort.