Query may return NULL columns if used in UNION ALL

[mtuncer]

This issue is reported in cstore_fdw forum at https://groups.google.com/forum/#!topic/cstore-users/oqsWZHtlL74

Query 1:

(SELECT A*1 , B FROM TEST_UNION_1 LIMIT 10) UNION ALL (SELECT A*1 , B FROM TEST_UNION_2 LIMIT 10);

Query 2:

(SELECT A*1 , B FROM TEST_UNION_1 ) UNION ALL (SELECT A*1 , B FROM TEST_UNION_2 );

Query 1 works fine but Query 2 returns NULL columns . This is because in "ColumnList" function has the following code snippet

if (neededColumn->varattno == columnIndex)
{   
    column = neededColumn;
    break;
}

Query 1 --- varattno is 1,2 for a,b
Query 2 --- varattno is 141,2 for a,b

So CStore doesn't consider Column "a" and hence the NULL values.

[sriharsha9992]

Hi ,

I have already fixed the issue . When the plan has APPEND state , PG includes Exprs in the targetColumnList. So , the 141 was actually a OPEXPR (int4mul) . To fix this , all we have to do is ,

REPLACE
List *targetColumnList =baserel->reltargetlist;

WITH
List *targetColumnList = pull_var_clause(baserel->reltargetlist, PVC_RECURSE_AGGREGATES, PVC_RECURSE_PLACEHOLDERS);

Regards,
Harsha