GSquared (9/24/2012)
Another possible:
IF OBJECT_ID(N'tempdb..#T') IS NOT NULLDROP TABLE #T;
CREATE TABLE #T
(EntryID INT NOT NULL,
EntryTime DATETIME NOT NULL,
FieldValue VARCHAR(MAX));
INSERT INTO #T
(EntryID, EntryTime, FieldValue)
VALUES (1, '20120924 00:00:00', 'We cannot do anything until 1 O''Clock - the penguin needs defrosting'),
(1, '20120924 13:00:00',
'We cannot do anything until 1 O''Clock - the penguin needs defrosting I have defrosted it'),
(1, '20120924 13:05:00',
'We cannot do anything until 1 O''Clock - the penguin needs defrosting I have defrosted it It''s Alive!'),
(1, '20120924 13:10:00',
'We cannot do anything until 1 O''Clock - the penguin needs defrosting I have defrosted it It''s Alive! I let it go.');
SELECT T1.EntryTime,
LTRIM(STUFF(T1.FieldValue, 1, ISNULL(LEN(Previous.FieldValue), 0), ''))
FROM #T AS T1
OUTER APPLY (SELECT TOP (1)
*
FROM #T AS T2
WHERE T1.EntryID = T2.EntryID
AND T1.EntryTime > T2.EntryTime
ORDER BY EntryTime DESC) AS Previous
ORDER BY T1.EntryTime;
Outer Apply grabs the immediately prior row, if any, gets the Len() of the value, and uses Stuff() to get rid of that much of the beginning of the string.
Using Replace() (as per Chris idea), might not work if a string can repeat itself inside the data. If, for example, the first entry were "Hello!", and the second were then "Hello! Hello! to you too", you'd end up with the "Hello!" substring stripped out where it's not supposed to be. If that's not a possible scenario (repeating string), then it won't matter and either will work.
Good point, Gus. First mental pass used STUFF but it flew away during coding.
-- sample data
DROP TABLE #Sample
CREATE TABLE #Sample (UserName VARCHAR(15), [Time] CHAR(8), FieldValue TEXT)
INSERT INTO #Sample (UserName, [Time], FieldValue)
SELECT 'Bob Hope', '12:00:00', 'We cannot do anything until 1 O''Clock - the penguin needs defrosting'
UNION ALL SELECT 'Rolf Harris', '13:00:00', 'We cannot do anything until 1 O''Clock - the penguin needs defrosting I have defrosted it'
UNION ALL SELECT 'Jeff Bridges', '13:13:00', 'We cannot do anything until 1 O''Clock - the penguin needs defrosting I have defrosted it It''s Alive!'
UNION ALL SELECT 'Jenny Bond', '13:46:25', 'We cannot do anything until 1 O''Clock - the penguin needs defrosting I have defrosted it It''s Alive! I let it go.'
-- solution
;WITH SequencedData AS (
SELECT
UserName,
[Time],
FieldValue = CAST(FieldValue AS VARCHAR(MAX)),
rn = ROW_NUMBER() OVER (ORDER BY [Time])
FROM #Sample
),
rCTE AS (
SELECT UserName, [Time], rn,
UserString = FieldValue,
FieldValue = FieldValue
FROM SequencedData
WHERE rn = 1
UNION ALL
SELECT tr.UserName, tr.[Time], tr.rn,
UserString = LTRIM(STUFF(tr.FieldValue,1,DATALENGTH(lr.FieldValue),'')),
FieldValue = tr.FieldValue
FROM SequencedData tr
INNER JOIN rCTE lr ON lr.rn+1 = tr.rn
)
SELECT UserName, [Time], UserString
FROM rCTE
For fast, accurate and documented assistance in answering your questions, please read this article.
Understanding and using APPLY, (I) and (II) Paul White
Hidden RBAR: Triangular Joins / The "Numbers" or "Tally" Table: What it is and how it replaces a loop Jeff Moden