case statement logic [closed]

问题

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Closed 8 years ago.

Let's make this easy.

I have a table.

visitID   studentname      dob       roll.no     value    displIndex     propID
200019      rob         05/18/1937     101      smoking       2             83
200019      rob         05/18/1937     101                    2             91
200019      rob         05/18/1937     101      alcohol       1             83
200019      rob         05/18/1937     101                    1             91
200020      henry       08/20/1987     102      smoking       2             83
200020      henry       08/20/1987     102                    2             91
200021      king        09/21/1982     103      alcohol       1             83
200021      king        09/21/1982     103                    1             91

I have a table of a similar kind.

Now what I am trying to do is if there is no display index of 1 for that particular visitID of that student, then in the case statement return a value of '779'.

select visitID,studentname
       ,dob
       ,roll.no
       ,value
       ,dispIndex
       ,propID
       ,case 
             WHEN (PATINDEX('%smoking%',value) >0 OR
                  (PATINDEX('%sometimes smoking%',value) > 0) THEN
                        '777'
              WHEN (PATINDEX(%not smoking%,value) >0 OR
                   (PATINDEX(%do not smoke%,value) >0_  THEN
                          '778'
             WHEN (ISNULL(CAST(value as varchar(max)),'')='') THEN
                          '779'
              ELSE
                          '779'
             END VALUE

Here King doesn't have a record under smoking. So I want it to go into the 779 bucket. How can I perform that?

回答1:

Not sure why you're doing a cast here (based on your sample data), so change this:

WHEN (ISNULL(CAST(value as varchar(max)),'')='') THEN '779'

To this:

WHEN ISNULL(value,'') = '' THEN '779'

Also -- realize that the way you're doing your wildcards, all of your 'not smoking' values are going to be '777' because they match the first pattern (PATINDEX('%smoking%',value) (i.e., the 2nd pattern won't even be checked).

EDIT
answers to your questions in the comment:

---

1) How will it pull the record of king-->smoking-->displayIndex 2?
Answer: There is no record in your sample set for King with a displayindex of 2. You can't pull a record that isn't there.

2) I want to check for ... alcohol records.
Answer: You already solved that problem for the smokers & non-smokers. Just do the same kind of thing for alchohol. For example: WHEN PATINDEX('%alchohol%',value) > 0 THEN '779'

3) I would like to put the king student under 779
Answer: He is. The way a CASE statement works, if none of the WHEN conditions evaluate to true (i.e., ...WHEN PATINDEX('%smoking%',value) > 0) then the ELSE statement is used. Since none of the WHEN statements will evaluate to true for King, he will be under 779.

来源：https://stackoverflow.com/questions/7122431/case-statement-logic