Re: Paged Query - Mailing list pgsql-performance

From Misa Simic
Subject Re: Paged Query
Date
Msg-id CAH3i69=B7VPj0rkbuxv9TLEF6V0DjB2xzcEUkf8U7BYULCOBug@mail.gmail.com
Whole thread Raw
In response to Paged Query  (Hermann Matthes <hermann.matthes@web.de>)
Responses Re: Paged Query  (Gregg Jaskiewicz <gryzman@gmail.com>)
List pgsql-performance
Hi Hermann,

Well,

Not clear how you get rows for user without paging?

If it is some query:

SELECT columns FROM table WHERE UserHasPerimision(rowPK, userid)

Paging would be:

SELECT columns FROM table WHERE UserHasPerimision(rowPK, userid) LIMIT NoOfRecords OFFSET page*NoOfRecords

Kind Regards,

Misa

2012/7/4 Hermann Matthes <hermann.matthes@web.de>
I want to implement a "paged Query" feature, where the user can enter in a dialog, how much rows he want to see. After displaying the first page of rows, he can can push a button to display the next/previous page.
On database level I could user "limit" to implement this feature. My problem now is, that the user is not permitted to view all rows. For every row a permission check is performed and if permission is granted, the row is added to the list of rows sent to the client.
If for example the user has entered a page size of 50 and I use "limit 50" to only fetch 50 records, what should I do if he is only permitted to see 20 of these 50 records? There may be more records he can view.
But if I don't use "limit", what happens if the query would return 5,000,000 rows? Would my result set contain 5,000,000 rows or would the performance of the database go down?

Thanks in advance
Hermann

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