DB2中的EXCEPT SELECT SQL查询

Question

I'm new to DB2 and couldn't find anything relating to EXCEPT queries [except] quite simple examples. I'm trying to compare values across two tables in order to return values which appear in TABLE_A but not in TABLE_B . The problem is that the columns being compared do not key exactly, but require some manipulation first.

ID_1 field from TABLE_A looks like this: 000 999

ID_2 field from TABLE_B looks like this: 111-000999

So by massaging the data from each ID we get the key value of 000999 for this sample row. This should result in this row being excluded from the query result as the data is present in both tables.

SELECT REPLACE (ID_1, ' ','') AS ID_1_TRIM
FROM MYDB.TABLE_A
EXCEPT 
SELECT SUBSTRING(ID_2,5,10) 
FROM MYDB.TABLE_B

This syntax doesn't work, it appears to return all the values in TABLE_A , even though the massaged key values also appear in TABLE_B .

Answer 1

have you try to trim may be

 SELECT trim(REPLACE (ID_1, ' ','')) AS ID_1_TRIM
 FROM MYDB.TABLE_A
 EXCEPT 
 SELECT trim(SUBSTRING(ID_2,5,10)) FROM MYDB.TABLE_B

or cast

 SELECT cast(trim(REPLACE (ID_1, ' ','')) as varchar(15)) AS ID_1_TRIM
 FROM MYDB.TABLE_A
 EXCEPT 
 SELECT cast(trim(SUBSTRING(ID_2,5,10)) as varchar(15))  FROM MYDB.TABLE_B

In my iseries your query work, are you sur it's space characteres in ID_1 ?