在外部表的元数据创建后，你可以直接和并发地查询外部表数据，这使得外部表像视图一样运行，无需将外部数据导入数据库。通过标准并发HINT和PARALLEL语句指定外部表的并发度，允许多个数据文件并行访问，从而提高数据访问效率。文件访问的并发度依赖于访问驱动实现和数据文件属性。
After the metadata for an external table is created, you can query the external data
directly and in parallel, using SQL. As a result, the external table acts as a view, which
lets you run any SQL query against external data without loading the external data
hints and with the PARALLEL clause. Using parallelism on an external table allows for
concurrent access to the datafiles that comprise an external table. Whether a single file
is accessed concurrently is dependent upon the access driver implementation, and
directly and in parallel, using SQL. As a result, the external table acts as a view, which
lets you run any SQL query against external data without loading the external data
into the database.
在外部表的元数据创建后，你可查询外部表数据直接地和并发地，通过使用SQL。结果就是，
外部表的行为像视图，它可以让你运行任何的SQL查询外部表数据而不需要导入外部表数据到
数据库中。
hints and with the PARALLEL clause. Using parallelism on an external table allows for
concurrent access to the datafiles that comprise an external table. Whether a single file
is accessed concurrently is dependent upon the access driver implementation, and
attributes of the datafile(s) being accessed (for example, record formats).
并发访问外部表的并发度的批定使用标准并发HINT使用PARALLEL语句。使用并发机制在一
个外部表允许并发的访问组成外部表的数据文件。一个单独文件是否被并发访问它取决于访问
驱动的执行，和被访问的数据文件的属性（比如记录格式）。
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