@ ("at" sign)
Runs the SQL*PLus statements in the specified script.
The script can be called from the local file system or from a web server.
@@ (double "at" sign)
Runs a script. This command is similar to the @ ("at" sign) command.
It is useful for running nested scripts because it looks for the specified script in
the same path as the script from which it was called.
@@表示调用和当前脚本同路径下SQL脚本文件。