SQL: Difference between rows

Question

I am trying to find the difference between two numbers corresponding to the same ID, but with two different conditions. For example,

Column A Column B Column C
1234     3         True 
1234     5         False
5678     10        True
5678     15        False

So basically i want to find the difference in Column B when column A is the same but Column C is different.

Answer 1

If we can assume

• 2 rows for a given value in ColumnA
• expected result is only 1 row returned per unique colA value
• columnC will never be null...
• Column B will never match, and if they do, you don't want the record returned.

We can use a self join checking for matches on column A, no matches on column C and so that we don't get a row each for 1234 of 2 and -2.

SELECT Z.ColumnA, Z.B-Y.B
FROM TableName Z
INNER JOIN tableName Y
 on Z.ColumnA = Y.ColumnA
and Z.ColumnC <> Y.ColumnC
and Z.ColumnB > Y.ColumnB

you could also do this with a window function using lead and look ahead to the next record. but I don't know if your RDBMS supports window functions.

Answer 2

 select t1.ColumnA, t1.ColumnB-t2.ColumnB diff from
 tab t1, tab t2
 where t1.columnA = t2.columnA and t1.ColumnC='True' and t2.ColumnC='False'

Answer 3

If your table name is myTable , I believe you can join the table with itself and on Column A and then select a difference in Column B when Column C is not equal to itself. So something like this

SELECT X.ColumnB - Y.ColumnB as Diff
FROM myTable as X
inner join
     myTable as Y
on X.ColumnA=Y.ColumnA
WHERE X.ColumnC <> Y.ColumnC

Answer 4

You could use a self join

  select a.column_A, a,column_B, b.column_B, a.column_B . b.column_B
  from my_table a 
  inner join my_column b where a.column_a = b.column_a and a.column_c <> b_column_c

Answer 5

If you RDBMS supports window functions

;with cte as (
    Select *
          ,Change    = ColumnB-Lag(ColumnB,1) over (Partition By ColumnA Order By (Select null))
          ,TrueFalse = Lag(ColumnC,1) over (Partition By ColumnA Order By (Select null))
    From @YourTable
)
Select ColumnA
      ,Change
 From  cte
 Where Change<>0
   and TrueFalse<>ColumnC

Returns

ColumnA Change
1234    2
5678    5

Answer 6

This one subtracts the "true" rows from the "false" rows, while preserving all true rows.

SELECT true.columna, true.columnb, COALESCE(false.columnb, 0) - true.columnb AS difference
FROM
(SELECT *
 FROM t
 WHERE columnc = "true") true
LEFT JOIN
(SELECT *
 FROM t
 WHERE columnc = "false) false
ON true.columna = false.columna

The coalesce clause will account for cases in which there is no false row. Without it you will end up trying to subtract from NULL.

Answer 7

If you're using Oracle, take a look at User Defined aggregate functions . If you define a function called diff() , then you can use select column_A, diff(column_B) from my_table group by column_A , but remember that the implementation of diff needs special care as different ordering will generate different results.