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https://issues.apache.org/jira/browse/CALCITE-5730?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17727738#comment-17727738
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Julian Hyde commented on CALCITE-5730:
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A test case (a chunk of java code added to Calcite's test suite) is definitely
required in the PR, but when the bug is logged it's useful to have a simple SQL
query that illustrates the problem. And a statement about what's wrong: "The
query returns 3 rows but should only return 2 because ...". That's what I meant
by "test case", but I didn't explain myself very well.
> Initial null values can be dropped by EnumerableLimitSort with offset
> ---------------------------------------------------------------------
>
> Key: CALCITE-5730
> URL: https://issues.apache.org/jira/browse/CALCITE-5730
> Project: Calcite
> Issue Type: Bug
> Components: linq4j
> Reporter: Feng Guo
> Priority: Major
> Labels: pull-request-available
> Fix For: 1.35.0
>
>
> *Description*
> The EnumerableSortLimit Node deals with offset with following logic:
> {code:java}
> // skip the first 'offset' rows by deleting them from the map
> if (offset > 0) {
> // search the key up to (but excluding) which we have to remove entries
> from the map
> int skipped = 0;
> TKey until = null;
> for (Map.Entry<TKey, List<TSource>> e : map.entrySet()) {
> skipped += e.getValue().size();
> if (skipped > offset) {
> // we might need to remove entries from the list
> List<TSource> l = e.getValue();
> int toKeep = skipped - offset;
> if (toKeep < l.size()) {
> l.subList(0, l.size() - toKeep).clear();
> }
> until = e.getKey();
> break;
> }
> }
> if (until == null) {
> // the offset is bigger than the number of rows in the map
> return Linq4j.emptyEnumerator();
> }
> map.headMap(until, false).clear();
> }
> {code}
> In a NULLS FIRST sort, if we set offset=1, limit = 1 when first 10 rows have
> null compare key, the until will be null. But that does not mean offset
> bigger than number of rows, it should have results instead of emptyEnumerator;
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