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https://issues.apache.org/jira/browse/TRAFODION-1575?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Selvaganesan Govindarajan updated TRAFODION-1575:
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Fix Version/s: (was: 2.3)
2.4
> Self-referencing update updates the column to a wrong value
> -----------------------------------------------------------
>
> Key: TRAFODION-1575
> URL: https://issues.apache.org/jira/browse/TRAFODION-1575
> Project: Apache Trafodion
> Issue Type: Bug
> Components: sql-cmp
> Affects Versions: 1.3-incubating
> Environment: Can be reproduced on a workstation
> Reporter: Dave Birdsall
> Assignee: Selvaganesan Govindarajan
> Priority: Major
> Fix For: 2.4
>
>
> As shown in the following execution output, the update statement tries to
> update c2 with count(distinct c2) from the same table. While the subquery
> ‘select c from (select count(distinct c2) from mytable) dt(c)’ returns the
> correct result 3 when it is run by itself, the update statement using the
> same subquery updated the column c2 to 2, instead of 3. The updated value
> always seems to be 1 less in this case.
> Here is the execution output:
> >>create schema mytest;
> --- SQL operation complete.
> >>
> >>create table mytable (c1 char(1), c2 integer);
> --- SQL operation complete.
> >>
> >>insert into mytable values ('A', 100), ('B', 200), ('C', 300);
> --- 3 row(s) inserted.
> >>select * from mytable order by 1;
> C1 C2
> -- -----------
> A 100
> B 200
> C 300
> --- 3 row(s) selected.
> >>select c from (select count(distinct c2) from mytable) dt(c);
> C
> --------------------
> 3
> --- 1 row(s) selected.
> >>
> >>prepare xx from update mytable set c2 =
> +>(select c from (select count(distinct c2) from mytable) dt(c))
> +>where c2 = 100;
> --- SQL command prepared.
> >>explain options 'f' xx;
> LC RC OP OPERATOR OPT DESCRIPTION CARD
> ---- ---- ---- -------------------- -------- -------------------- ---------
> 12 . 13 root x 1.00E+001
> 10 11 12 tuple_flow 1.00E+001
> . . 11 trafodion_insert MYTABLE 1.00E+000
> 9 . 10 sort 1.00E+001
> 8 4 9 hybrid_hash_join 1.00E+001
> 6 7 8 nested_join 1.00E+001
> . . 7 trafodion_delete MYTABLE 1.00E+000
> 5 . 6 sort 1.00E+001
> . . 5 trafodion_scan MYTABLE 1.00E+001
> 3 . 4 sort_scalar_aggr 1.00E+000
> 2 . 3 sort_scalar_aggr 1.00E+000
> 1 . 2 hash_groupby 2.00E+000
> . . 1 trafodion_scan MYTABLE 1.00E+002
> --- SQL operation complete.
> >>execute xx;
> --- 1 row(s) updated.
> >>
> >>select * from mytable order by 1;
> C1 C2
> -- -----------
> A 2
> B 200
> C 300
> --- 3 row(s) selected.
> >>
> >>drop schema mytest cascade;
> --- SQL operation complete.
> >>
> The value of C2 in row A above should have been updated to 3.
> This problem was found by Wei-Shiun Tsai.
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