sql oracle how to count value increases in column

Question

I need help counting the number of times a column's value increased and decreased for a certain ID.

I have data that looks like this

ID  Month   Value1  
1   1   500  
1   2   500  
1   3   500  
1   4   1000  
2   1   1000  
2   2   500  
2   3   500  
2   4   1000  
3   1   6000  
3   2   6000  
3   3   5000  
3   4   5000  

And I want this

ID  Increases   Decreases  
1   1   0  
2   1   1  
3   0   1  

Thank you!

Answer 1

Create a calculated column using the lead function which gets the values from the next row. Then aggregate based on the calculated column.

select id,
count(case when inc_or_dec = 'increase' then 1 end) increases,
count(case when inc_or_dec = 'decrease' then 1 end) decreases
from (
select id,
case 
when coalesce(lead(value1) over(partition by id order by mth),value1) > value1 then 'increase'
when coalesce(lead(value1) over(partition by id order by mth),value1) < value1 then 'decrease'
when coalesce(lead(value1) over(partition by id order by mth),value1) = value1 then 'no change'
end inc_or_dec
from tablename) t
group by id

Answer 2

Only for fun ;) with sign function:

  SELECT id, SUM (SIGN (di + 1)) incCount, SUM (SIGN (di - 1)*-1) decCount
    FROM (SELECT id, SIGN (LEAD (value1, 1) OVER (PARTITION BY id ORDER BY id, month) - value1) di FROM TABLENAME)
   WHERE di <> 0
GROUP BY id

Answer 3

Here is a solution based on the lag window aggregate function:

SELECT   id,
         count(CASE WHEN value > prev_value THEN 1 END) Increases,
         count(CASE WHEN value < prev_value THEN 1 END) Decreases
FROM     (SELECT id,
                 month,
                 value,
                 lag(value) OVER (PARTITION BY id ORDER BY month) AS prev_value
          FROM   mytable)
GROUP BY id

If you just run the inner query, you can see how it puts the previous value next to the current value in each record.