Thread

1. Incorrect sort result caused by ROLLUP and WHERE operation

   谭忠涛 <zhongtao.tan@seaboxdata.com> — 2025-01-02T07:28:25Z

   Case:
   create table t1(a int, b int);
   insert into t1 values(1,1),(1,2);
   select a,b,sum(10) as s from t1 where a = 1 group by rollup(a,b) order by a, s desc;
   
   
   
   
   
   
   
   Regards
   
   
   
   谭忠涛   数据研究院数据库事业部
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2. Re: Incorrect sort result caused by ROLLUP and WHERE operation

   Zhang Mingli <zmlpostgres@gmail.com> — 2025-01-02T10:49:26Z

   Hi,
   
   
   Zhang Mingli
   www.hashdata.xyz
   
   Do you mean order of null value (column a)  is wrong?
   Use NULLS FIRST/LAST to order null values.
   On Jan 2, 2025 at 18:19 +0800, 谭忠涛 <zhongtao.tan@seaboxdata.com>, wrote:
   >
   > Case:
   > create table t1(a int, b int);
   > insert into t1 values(1,1),(1,2);
   > select a,b,sum(10) as s from t1 where a = 1 group by rollup(a,b) order by a, s desc;
   

3. Re: Incorrect sort result caused by ROLLUP and WHERE operation

   Tom Lane <tgl@sss.pgh.pa.us> — 2025-01-02T16:04:23Z

   "=?utf-8?B?6LCt5b+g5rab?=" <zhongtao.tan@seaboxdata.com> writes:
   > create table t1(a int, b int);
   > insert into t1 values(1,1),(1,2);
   > select a,b,sum(10) as s from t1 where a = 1 group by rollup(a,b) order by a, s desc;
   
   Yeah.  This is fixed in HEAD (v18-to-be) but the fix is too invasive
   to consider back-patching.  Basically the problem is that older
   versions don't understand that the post-ROLLUP value of "a" can be
   different from the pre-ROLLUP value, so they think the "where a = 1"
   clause removes any need to sort by "a".
   
   As a workaround you could write something like "order by a+0, s desc"
   to fool the optimizer into considering the ordering column to be
   different from the value that's constrained by WHERE.
   
   			regards, tom lane