使用 UNION ALL 运算符获取忽略 null 的结果

Question

Here is my code:

select TRANSACTIONID, INFORMATION as "C_cntct", NULL as "C_nam"
from RETAILTRANSACTIONINFOCODETRANS as t
where INFOCODEID = 1009 and TRANSDATE = '2022-07-20'

UNION

select TRANSACTIONID, NULL, INFORMATION
from RETAILTRANSACTIONINFOCODETRANS as t
where INFOCODEID = 1010 and TRANSDATE = '2022-07-20'
group by TRANSACTIONID, INFORMATION
order by TRANSACTIONID, INFORMATION desc

I am getting result is:

TRANSACTIONID	C_cntct	C_nam
ST-EMP-ST-LHR-01-66079	RASHID ALI	NULL
ST-EMP-ST-LHR-01-66079	NULL	0321-9439143
ST-EMP-ST-LHR-01-66080	SADAFSEHAR	NULL
ST-EMP-ST-LHR-01-66080	NULL	0345-4036448

But I want this result, with Null Ignore:

TRANSACTIONID	C_cntct	C_nam
ST-EMP-ST-LHR-01-66079	RASHID ALI	0321-9439143
ST-EMP-ST-LHR-01-66080	SADAFSEHAR	0345-4036448

Answer 1

Sounds like you need conditional aggregation (aka Pivot), although without sample input data it's hard to say for sure.

It's generally simpler to just use MIN(CASE WHEN for this, rather than using the explicit PIVOT syntax, which is rather limited.

SELECT
  trans.TRANSACTIONID,
  MIN(CASE WHEN trans.INFOCODEID = 1009 THEN trans.INFORMATION END) AS C_cntct,
  MIN(CASE WHEN trans.INFOCODEID = 1010 THEN trans.INFORMATION END) AS C_nam
FROM RETAILTRANSACTIONINFOCODETRANS AS trans
WHERE trans.INFOCODEID IN (1009, 1010)
  AND trans.TRANSDATE = '2022-07-20'
GROUP BY
  trans.TRANSACTIONID
ORDER BY
  trans.TRANSACTIONID;