为什么我不认为case语句返回NULL值？

Question

Question is at the bottom but in short, the table I'm creating is giving my Null values for the field Division even when the links match my case expression and I cant seem to find why.

I am creating a table to assign divisions according to a link url within the program:

create table set_divisions as
  select distinct campaign, offer,
   case
   when upper(link) like '%NORTH%' then 'NORTH'
   when upper(link) like '%SOUTH%' then 'SOUTH'
   when upper(link) like '%EAST%'  then 'EAST'
   when upper(link) like '%WEST%'  then 'WEST'
   ELSE NULL
   END AS DIVISION
   FROM TABLE A;

I then get a lot of NULL's in Division so I'm trying to see what links I'm missing as they all should have a value in Division. Each campaign does have multiple links some not associated with north, south, east or west but every campaign should also contain one of these links from the case statement.

I then run the following:

select distinct link
from  A, set_divisions S
where A.campaigncode = S.campaigncode
and   A.offercode    = S.offercode
and (
     upper(link) like '%NORTH%'
     or upper(link) like '%SOUTH%'
     or upper(link) like '%EAST%'
     or upper(link) like '%WEST%');

The results come back with links that have NORTH , SOUTH , EAST AND WEST in them.

So my question is what am I doing wrong in my case expression when creating my table, that is causing it to miss these links?

examples of links being missed are(I only used south and east but there are similar links for all four):

http://product.south.com/information/preference
http://sports.east.com/unsubscribe/?email=%%Linkurl9%%

Thanks and this is my first post so I apologize ahead of time if I missed something or my code looks crappy lol.

Reighlo

Answer 1

In the second query, your WHERE clause specifies that link must contain NORTH, SOUTH, EAST, or WEST. Your first query does not contain a similar WHERE clause.

You can run this to find links not containing NORTH, SOUTH, EAST or WEST to troubleshoot:

select distinct link
from  A, set_divisions S
where A.campaigncode = S.campaigncode
and   A.offercode    = S.offercode
and upper(link) not like '%NORTH%'
and upper(link) not like '%SOUTH%'
and upper(link) not like '%EAST%'
and upper(link) not like '%WEST%');

Answer 2

So the table that I was running this for had tens of millions of rows and as mentioned in the comments above the case statement was bringing back Null due to many rows that yielded that result even if my link url was in there. I did not want to exclude all that resulted in NULL because there are some programs that truly should be null. I found that by bringing in all rows with their urls and grouping them, then selecting distinct values from that subset with my case statement included, then selecting again and running the case statement for all the remaining where division is still null did the trick. However, this did bring back duplicates so I had to use rownumber() to bring in everything I wanted. Basically to get rid of any NULL's where a true division already existed. There were some duplicates with different divisions but I needed to bring those in because that's another issue that has to be looked at. Here is my code and please feel free to let me know if there was an easier way to do this. Not sure if it matters but my table ran in about 5 minutes. Sorry if there are any typos, I had to recreate from my code to the fields and values here because our client is real big on privacy issues and although this would not put anything out there, it's just a headache I'd rather not deal with.

create table set_divisions as       
SELECT DISTINCT CAMPAIGNCODE, OFFERCODE, DIV        
FROM
(
    SELECT DISTINCT CAMPAIGN, OFFER, DIVISION
    ROWNUMBER() OVER
    (PARTITION BY CAMPAIGNCODE, OFFERCODE, ORDER BY DIVISION) AS RN
    FROM (SELECT DISTINCT CAMPAIGN, OFFER, DIVISION)
                case
                when upper(URL) like '%NORTH%'
                AND DIVISION IS NULL THEN 'NORTH'
                when upper(URL) like '%SOUTH%' 
                AND DIVISION IS NULL then 'SOUTH'
                when upper(URL) like '%EAST%'  
                AND DIVISION IS NULL then 'EAST'
                when upper(URL) like '%WEST%'  
                AND DIVISION IS NULL then 'WEST'
                ELSE DIVISION
                END AS DIV      
    FROM
    (
        SELECT DISTINCT CAMPAIGN, OFFER, DIVISION,
        CASE WHEN DIVISION IS NULL THEN LINK_URL
        ELSE NULL 
        END AS URL          
        FROM 
            (
                select campaign, offer, linkurl
                case
                when upper(link) like '%NORTH%' then 'NORTH'
                when upper(link) like '%SOUTH%' then 'SOUTH'
                when upper(link) like '%EAST%'  then 'EAST'
                when upper(link) like '%WEST%'  then 'WEST'
                ELSE NULL
                END AS DIVISION
                FROM TABLE A
                group by campaign, offer, linkurl
                case
                when upper(link) like '%NORTH%' then 'NORTH'
                when upper(link) like '%SOUTH%' then 'SOUTH'
                when upper(link) like '%EAST%'  then 'EAST'
                when upper(link) like '%WEST%'  then 'WEST'
            )               
    )                       
)   
    WHERE RN = 1
    OR (RN >1
        AND DIV IS NOT NULL);