SQL在Union语句中使用Order By

Question

Please see below code i am struggling with:

select * 
from AAA_PROD_XEUSS.P_E_LVR_CQT CQT 
left join AAA_PROD_XEUSS.P_F_OPERATION OPER
on CQT.OPERATION = OPER.OPERATION
union
select * 
from BBB_PROD_XEUSS.P_E_LVR_CQT CQT
left join BBB_PROD_XEUSS.P_F_OPERATION OPER
on CQT.OPERATION = OPER.OPERATION
where CQT.PROCESS = '1111'
Order by OPERATION

I am getting following Error: ERROR [42877] [IBM][DB2/LINUXX8664] SQL0197N A qualified column name is not allowed in the ORDER BY clause. Any suggested solution giving errors

Thank you

Answer 1

Take the order by clause outside, and alias all the columns in the select lists of inner part.

( One of cqt.operation or oper.operation may be preferred inside, since they're matched to be equal ) :

Select * 
from
    (select cqt.col1, cqt.col2, oper.* 
     -- where "operation" column is exempted from cqt list, 
     --  since the table aliased as oper already has "operation" column.
     from AAA_PROD_XEUSS.P_E_LVR_CQT CQT 
     left join AAA_PROD_XEUSS.P_F_OPERATION OPER on CQT.OPERATION = OPER.OPERATION
     union
     select cqt.col1, cqt.col2, oper.*
     from BBB_PROD_XEUSS.P_E_LVR_CQT CQT
     left join BBB_PROD_XEUSS.P_F_OPERATION OPER on CQT.OPERATION = OPER.OPERATION
     where CQT.PROCESS = '1111'
) 
Order by OPERATION

Answer 2

You can use the order by , but you need to list the columns explicitly. This is a good practice anyway:

select cqt.*, oper.?, oper.?, . . .
from AAA_PROD_XEUSS.P_E_LVR_CQT CQT left join
     AAA_PROD_XEUSS.P_F_OPERATION OPER
    on CQT.OPERATION = OPER.OPERATION
union
select cqt.*, oper.?, oper.?, . . .
from BBB_PROD_XEUSS.P_E_LVR_CQT CQT left join
     BBB_PROD_XEUSS.P_F_OPERATION OPER
     on CQT.OPERATION = OPER.OPERATION
where CQT.PROCESS = '1111'
Order by OPERATION;

The OPERATION column should be coming from the CQT table. The ? s are placeholders for additional columns in OPER . This assumes that the two CQT tables have the same columns with the same types defined in the same order. The better practice is to list all columns.

Answer 3

If you are using Db2 11.1, you can use the JOIN USING syntax to avoid having two copies of the joined column(s) in the result set https://www.ibm.com/support/knowledgecenter/en/SSEPGG_11.1.0/com.ibm.db2.luw.sql.ref.doc/doc/r0059207.html

Eg with these tables

create table AAA_PROD_XEUSS.P_E_LVR_CQT   (i int, OPERATION int, PROCESS char(4)););
create table AAA_PROD_XEUSS.P_F_OPERATION (b int, OPERATION int);
create table BBB_PROD_XEUSS.P_E_LVR_CQT   (c int, OPERATION int, PROCESS char(4));
create table BBB_PROD_XEUSS.P_F_OPERATION (b int, OPERATION int);

this select

select * 
from AAA_PROD_XEUSS.P_E_LVR_CQT CQT 
left join AAA_PROD_XEUSS.P_F_OPERATION OPER
USING ( OPERATION )
union
select * 
from BBB_PROD_XEUSS.P_E_LVR_CQT CQT
left join BBB_PROD_XEUSS.P_F_OPERATION OPER
USING ( OPERATION )
where CQT.PROCESS = '1111'
Order by OPERATION

Will return just one column named OPERATION

OPERATION I PROCESS B
--------- - ------- -

0 record(s) selected.

PS You might prefer to use UNION ALL rather than just UNION to avoid Db2 having to sort all the rows to remove duplicates