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Editorial Team
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Asked: 2026-06-17T21:37:41+00:00

I have this table where I only want to look at AB ID CODE

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I have this table where I only want to look at AB

ID     CODE       COUNT   
102    AB         9
101    AB         8
100    AC         23    //not important!!!!
99     AB         7
98     AB         6
97     AB         5
96     AB         0

Conversed to this

ID    NEWID     CODE       COUNT   
102   102       AB         9
101   101       AB         8
99    100       AB         7
98    99        AB         6
97    98        AB         5
96    97        AB         0

Using

SELECT
t.ID, t.CODE, t.COUNT,
@PREVCOUNT - t.COUNT DIFFERENCE,
@PREVCOUNT := t.COUNT  -- Updates for the next iteration, so it
                       -- must come last! 
FROM
(SELECT ID, CODE, COUNT FROM some_table WHERE CODE = 'AB' ORDER BY ID DESC) t,
(SELECT @PREVCOUNT := NULL) _uv;

http://sqlfiddle.com/#!2/e0b8b/36/0

So

Step 1: 9 - 1 = 1
Step 2: 8 - 7 = 1
Step 3: 7 - 6 = 1
Step 4: 6 - 5 = 1
Step 5: 5 - 0 = 5

Now there could be a case where I have 

ID    NEWID     CODE       COUNT   
102   102       AB         4
101   101       AB         2
99    100       AB         1
98    99        AB         0
97    98        AB         7
96    97        AB         0

Then I want to count

Step 1: 4 - 2 = 2
Step 2: 2 - 1 = 1
Step 3: 1 - 0 = 1
Step 4: 0 - 7 = -7      //want  to discard this negative value
Step 5: 5 - 0 = 7

Where I want to discard step 4 because this is negative.

Now I use this code to discard the negative value

SELECT
t.ID, t.CODE, t.COUNT,
@PREVCOUNT,
@PREVCOUNT - t.COUNT DIFFERENCE,
CASE @PREVCOUNT - t.COUNT WHEN @PREVCOUNT - t.COUNT >= 0 THEN 'equal or bigger' ELSE 'smaller' END,
@PREVCOUNT := t.COUNT  -- Updates for the next iteration, so it
                       -- must come last!
FROM
(SELECT ID, CODE, COUNT FROM some_table WHERE CODE = 'AB' ORDER BY ID DESC) t,
(SELECT @PREVCOUNT := NULL) _uv;

After executing this code I expect to see where the comparison made is bigger as or equal to 0, instead I get very different results.

Below a link to see what I mean:

http://sqlfiddle.com/#!2/6be4a/1

I would really like to know what is going wrong here, and I would love to have a solution.

Kind regards

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1 Answer

  1. Editorial Team

    How about this:

    http://sqlfiddle.com/#!2/6be4a/7

    select * from (
SELECT
    t.ID, t.CODE, t.COUNT,
    @PREVCOUNT,
    @PREVCOUNT - t.COUNT DIFFERENCE,
    CASE @PREVCOUNT - t.COUNT WHEN @PREVCOUNT - t.COUNT >= 0 THEN 'equal or bigger' ELSE 'smaller' END,
    @PREVCOUNT := t.COUNT  -- Updates for the next iteration, so it
                           -- must come last!
FROM
    (SELECT ID, CODE, COUNT FROM some_table WHERE CODE = 'AB' ORDER BY ID DESC) t,
    (SELECT @PREVCOUNT := NULL) _uv
group by t.id, t.code
)x
where x.difference >= 0;
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