文档解释
ORA-01409: NOSORT option may not be used; rows are not in ascending order
Cause: Creation of index with NOSORT option when rows were not ascending. For non-unique indexes the rowid is considered part of the index key. Therefore, if you create an index nosort and two of the rows in the table have the same key and are stored in ascending order, but get split accross two extents where the dba of the first block in the second extent is less than the dba of the last block in the first extent, then the create index nosort may fail.
Action: Create the index without the NOSORT option, or ensure table is stored in one extent.
这个错误表明在 Oracle 数据库中使用了NOSORT 选项，而NOSORT选项的使用必须确保结果行在升序中。
官方解释
ORA-01409 背景细节
当 NOSORT 选项用于在 SELECT 语句中指定的 ORDER BY 子句时，Oracle 数据库会抛出 ORA-01409：NOSORT 选项不能被使用。
发生这种情况原因是指定的 ORDER BY 子句不能确保在输出中结果行在升序中。
常见案例
SELECT employee_id
FROM employees
ORDER BY employee_id DESC NOSORT;
正常处理方法及步骤
1. 检查 SELECT 子句中 ORDER BY 子句后嵌入的 NOSORT 选项，确定是否需要。如果需要，则需要重新编写查询语句，确保结果行在升序中。
2. 去掉 NOSORT 选项，如果查询语句中SELECT 子句中 ORDER BY 子句没有出现 NOSORT 选项，则需要重新编辑表，以确保结果行是按指定的顺序排列。
