[Koha-bugs] [Bug 35966] New: Koha should not strip limits from SQL queries

[bugzilla-daemon at bugs.koha-community.org]

https://bugs.koha-community.org/bugzilla3/show_bug.cgi?id=35966

            Bug ID: 35966
           Summary: Koha should not strip limits from SQL queries
 Change sponsored?: ---
           Product: Koha
           Version: master
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P5 - low
         Component: Reports
          Assignee: koha-bugs at lists.koha-community.org
          Reporter: andrewfh at dubcolib.org
        QA Contact: testopia at bugs.koha-community.org
                CC: nick at bywatersolutions.com

Koha removes LIMIT from queries in some cases, which can cause incorrect
results. For example, consider this report to give the 5 oldest items in the
collection, sorted into callnumber order:
SELECT *
FROM (
SELECT itemnumber, cn_sort, dateaccessioned
FROM items
ORDER BY dateaccessioned
LIMIT 5
) foo
ORDER BY cn_sort

That query should get all the items, put them in dateaccessioned order, drop
all but the first 5, and then put those 5 in cn_sort order.

But Koha processes that by dropping the LIMIT and then re-applying it at the
end:
SELECT *
FROM (
SELECT itemnumber, cn_sort, dateaccessioned
FROM items
ORDER BY dateaccessioned
) foo
ORDER BY cn_sort
LIMIT 5

That makes the query get all the items, put them in dateaccessioned order, then
put them in cn_sort order, then drop all but the first 5. It changes the query
hugely. 

It only does this in queries without a WHERE, so that first query can be made
to work by editing it to: 

SELECT *
FROM (
SELECT itemnumber, cn_sort, dateaccessioned
FROM items
ORDER BY dateaccessioned
LIMIT 5
) foo
WHERE 1=1
ORDER BY cn_sort

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