Oracle recursive performance prompt

When you use start with connect by nocycle prior

When performing recursive data search

So the performance of the following two sections of code must be significantly different when you use it, please note that the code can be directly read below to view my summary

// Query the number of layers in a folder ID = 12 and the number of files

A: indicates the parent-subordinate relationship between files.

B: The file in the folder.

Positive Solution:

Select count (0) cou, max (levels) + 1 as levels

Select C. a1, C. a2, C. levels...

From

(Select A. a1, A. a2 ,,,

Level levels // hierarchy

From

Where A. a1 = ,,,

And A. a2 = ....

Start with A. a1 = 12

Connect by nocylce prior A. ID = A. ParentID

) C left join B

On C. File ID = B. File ID

And C. file type = folder

Error code:

Select count (0) cou, max (levels) + 1 as levels

Select C. a1, C. a2, C. levels...

From

(Select A. a1, A. a2 ,,,

Level levels // hierarchy

From

Left join B

On C. File ID = B. File ID

Where C. file type = folder

And A. a1 = ,,,

And A. a2 = ....

Start with A. a1 = 12

Connect by nocylce prior A. ID = A. ParentID

) C

The difference between the above Code is that

The correct method is:

Recursively loop all the folders and files under a folder

Search for the file content in the associated file table

The error is:

First, find the folder and file under a folder.

Then recursively loop out all the folders and files in the folder below him.

In this way, the redundant data after Association is generated. Loop recursion is performed together. It has nothing to do with the file. Shouldn't it? The file is also put in recursion.