How to increment DateTime column by a second for every row? - sql

Question

Suppose that I have this Time value: 09:00:00
And I have a table with a column Time, and I have three records in it.
I want to update those 3 records with that time but with the Time value incremented in one second each time (for every record).
Something like this:
ColumnA ColumnB
1 09:00:00
2 09:00:01
3 09:00:02
How can I do that?
My Solution:
After some time working on my own solution, this is what I came up with
update tor1
set ColumnB = dateadd(s,tor2.inc, ColumnB)
from table1 tor1
inner join (select ColumnA, ROW_NUMBER() OVER (Order by ColumnA) as inc from table1) tor2 on tor1.ColumnA=tor2.ColumnA

Answer 1

You don't specify any particular ordering.
For undeterministic/undocumented results you could try the quirky update approach.
CREATE TABLE table1
(
ColumnB datetime NULL
);
INSERT INTO table1 DEFAULT VALUES;
INSERT INTO table1 DEFAULT VALUES;
INSERT INTO table1 DEFAULT VALUES;
DECLARE #ColumnB datetime;
SET #ColumnB = '19000101 09:00:00';
UPDATE table1
SET #ColumnB = ColumnB = DATEADD(s, 1, #ColumnB);
SELECT *
FROM table1;
DROP TABLE table1;
Otherwise you will need to use a cursor or find some way of simulating ROW_NUMBER in 2000.

Answer 2

Here's a version that uses a #temp table but doesn't use the unsupported quirky update (no offense Martin) and doesn't rely on magical identity ordering, which is not guaranteed (no offense Richard).
CREATE TABLE dbo.Whatever
(
ColumnA INT IDENTITY(1,1),
ColumnB DATETIME
);
INSERT dbo.Whatever(ColumnB) SELECT '09:00';
INSERT dbo.Whatever(ColumnB) SELECT '09:00';
INSERT dbo.Whatever(ColumnB) SELECT '09:00';
INSERT dbo.Whatever(ColumnB) SELECT '09:00';
INSERT dbo.Whatever(ColumnB) SELECT '09:00';
-- just to demonstrate a gap
DELETE dbo.Whatever WHERE ColumnA = 3;
SELECT w.ColumnA, w.ColumnB,
c = (SELECT COUNT(*) FROM dbo.Whatever WHERE ColumnA < w.ColumnA)
INTO #x
FROM dbo.Whatever AS w;
UPDATE w
SET ColumnB = DATEADD(SECOND, x.c, w.ColumnB)
FROM dbo.Whatever AS w
INNER JOIN #x AS x
ON x.ColumnA = w.ColumnA;
SELECT ColumnA, ColumnB FROM dbo.Whatever;
Results:
ColumnA ColumnB
------- -----------------------
1 1900-01-01 09:00:00.000
2 1900-01-01 09:00:01.000
4 1900-01-01 09:00:02.000
5 1900-01-01 09:00:03.000

Answer 3

If you can assume ColumnA is the number of seconds you need to add (or directly proportional like your example), then you can use that.
UPDATE myTable SET ColumnB = DATEADD(s, (ColumnA - 1), ColumnB)
If not, you will need to determine the rank of each column (plenty of results on google for that) and add the rank instead.

Answer 4

For SQL Server 2005 onwards, you can use the OVER clause to control the ordering of the updates.
;with T as (
    select *, rn=row_number() over (order by columnA)
    from Tbl)
update T
   set columnB = DateAdd(s, rn-1, '09:00:00');
SQL Fiddle
For SQL Server 2000, you can use a temporary table. Use INSERT INTO..SELECT to guarantee the computation of the IDENTITY column.
CREATE TABLE table1
(
ColumnA int,
ColumnB datetime NULL
);
INSERT INTO table1 values (1, null);
INSERT INTO table1 values (2, getdate());
INSERT INTO table1 values (3, '02:02:02');
create table #tmp (ColumnA int, ID int identity(0,1))
insert into #tmp
select ColumnA
from table1
order by ColumnA;
update a
set ColumnB = dateadd(s,t.ID,'09:00:00')
from #tmp t
join table1 a on a.ColumnA = t.ColumnA;
select * from table1;