What language are you using? Usually there is iterator with chunked fetch option (like setFetchSize in java jdbc). So you are passing query without limit and then read as many results as you need. Note that query plan in this case won't be optimized for your limit and I don't remember if postgres has "optimize for N rows" statement option.
Also, if your statement is ordered by some key, you can use general paging technique when you rerun query with "key>max_prev_value" filter to get next chunk.
Середа, 4 липня 2012 р. користувач Hermann Matthes <hermann.matthes@xxxxxx> написав:
> 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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Best regards,
Vitalii Tymchyshyn
