MySql数据库设计-哪种表结构更好？

Question

I am working on a mysql database and would like to know which of these two table structures is better in terms of performance.

Structure 1; two tables with lots of common fields

table1(file)   : id, userid, parentid, name, desc, tags, public, dateadded, datemodified, linkid, domain, url, snapshot
table2(folder): id, userid, parentid, name, desc, tags, public, dateadded, datemodified, hasSubFolders, noOfItems, noOfViews

Structure 2; three tables with all the common fields put in a different table

table1(main)   : id, userid, parentid, objectid, objecttype(file or folder), name, desc, tags, public, dateadded, datemodified
table2(file)   : id (objectid), linkid, domain, url, snapshot
table3(folder) : id (objectid), hasSubFolders, noOfItems, noOfViews

Answer 1

I would use neither of them but something similar to the first example. There are a lot of common columns in the two tables. Therefore, two tables would have to be accessed just for a listing command ( ls in UNIX, dir ind Windows). Also, there are hints to the data-types in the column-names which is bad practice:

Instead, use one table: fsys_entries:

id, is_directory, parentid, name, desc, tags, public, added, modified, linkid, url, snapshot

With this structure it would be possible to create files and directories within files but with the correct restrictions from the code that is not a problem.

EDIT: In a real file-system a directory is a file with a directory-flag to it. So from that perspective its not too bad and it allows a more similar treatment as compared to a real file-system.

PS: As an advanced feature i would store the sharing-information (is the file/directory public? what link refers to it?) in a different table (which is just best practice).

Answer 2

If it performs comparably to the flat structure1, I'd go for Structure2 after renaming "main" to "FileSystemObject" or something more telegraphic.

The disadvantage is that you need joins for accessing the full information on any given FSO and this makes indexing more difficult (not sure if mysql supports indexed views nowadays).

In case of doubt, populate sample tables and benchmark.