Sql-server – Calculate Time Difference Between Two Rows

databasedifference-between-rowssql server

I have a table that contains the following:

DataDate                 Value
2010-03-01 08:31:32.000  100
2010-03-01 08:31:40.000  110
2010-03-01 08:31:42.000  95
2010-03-01 08:31:45.000  101
.                        .
.                        .
.                        .

I need to multiply the value column by the difference in time between the current and previous rows and sum that for the entire day.

I currently have the data set up to come in every 10 seconds which makes for a simple conversion in the query:

SELECT Sum((Value/6) FROM History WHERE DataDate BETWEEN @startDate and @endDate

Where @startDate and @endDate are today's date at 00:00:00 and 11:59:59.

Before I set the data to be collected every 10 seconds it was collected whenever the Value changed. There aren't any duplicate entries in terms of time, the minimum time difference is 1 second.

How can I set up a query to get the elapsed time between rows for the case when I don't know the time interval between readings?

I am using SQL Server 2005.

Best Answer

WITH    rows AS
        (
        SELECT  *, ROW_NUMBER() OVER (ORDER BY DataDate) AS rn
        FROM    mytable
        )
SELECT  DATEDIFF(second, mc.DataDate, mp.DataDate)
FROM    rows mc
JOIN    rows mp
ON      mc.rn = mp.rn - 1

In SQL Server 2012+:

SELECT  DATEDIFF(second, pDataDate, dataDate)
FROM    (
        SELECT  *,
                LAG(dataDate) OVER (ORDER BY dataDate) pDataDate
        FROM    rows
        ) q
WHERE   pDataDate IS NOT NULL

Related Solutions

Sql-server – How to remove duplicate rows

Assuming no nulls, you GROUP BY the unique columns, and SELECT the MIN (or MAX) RowId as the row to keep. Then, just delete everything that didn't have a row id:

DELETE FROM MyTable
LEFT OUTER JOIN (
   SELECT MIN(RowId) as RowId, Col1, Col2, Col3 
   FROM MyTable 
   GROUP BY Col1, Col2, Col3
) as KeepRows ON
   MyTable.RowId = KeepRows.RowId
WHERE
   KeepRows.RowId IS NULL

In case you have a GUID instead of an integer, you can replace

MIN(RowId)

with

CONVERT(uniqueidentifier, MIN(CONVERT(char(36), MyGuidColumn)))

Sql – the difference between “INNER JOIN” and “OUTER JOIN”

Assuming you're joining on columns with no duplicates, which is a very common case:

An inner join of A and B gives the result of A intersect B, i.e. the inner part of a Venn diagram intersection.
An outer join of A and B gives the results of A union B, i.e. the outer parts of a Venn diagram union.

Examples

Suppose you have two tables, with a single column each, and data as follows:

Note that (1,2) are unique to A, (3,4) are common, and (5,6) are unique to B.

Inner join

An inner join using either of the equivalent queries gives the intersection of the two tables, i.e. the two rows they have in common.

select * from a INNER JOIN b on a.a = b.b;
select a.*, b.*  from a,b where a.a = b.b;

a | b
--+--
3 | 3
4 | 4

Left outer join

A left outer join will give all rows in A, plus any common rows in B.

select * from a LEFT OUTER JOIN b on a.a = b.b;
select a.*, b.*  from a,b where a.a = b.b(+);

a |  b
--+-----
1 | null
2 | null
3 |    3
4 |    4

Right outer join

A right outer join will give all rows in B, plus any common rows in A.

select * from a RIGHT OUTER JOIN b on a.a = b.b;
select a.*, b.*  from a,b where a.a(+) = b.b;

a    |  b
-----+----
3    |  3
4    |  4
null |  5
null |  6

Full outer join

A full outer join will give you the union of A and B, i.e. all the rows in A and all the rows in B. If something in A doesn't have a corresponding datum in B, then the B portion is null, and vice versa.

select * from a FULL OUTER JOIN b on a.a = b.b;

 a   |  b
-----+-----
   1 | null
   2 | null
   3 |    3
   4 |    4
null |    6
null |    5

Best Answer

Related Solutions

Sql-server – How to remove duplicate rows

Sql – the difference between “INNER JOIN” and “OUTER JOIN”

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