2009-10-21
5,076 reads
T-SQL
2009-10-19
3,627 reads
Causation, Correlation and Crackpots
Joe Celko explores the dangers of muddling correlation and causation, emphasises the importance of determining how likely it is that a correlation has occurred by chance, and gets stuck into calculating correlation coefficients in SQL. Along the way, Joe illustrates the consequences of leaping to the wrong conclusion from correlations with tales of Pop Dread.
2009-10-19
2,136 reads
2009-10-16
5,095 reads
2009-10-14
4,691 reads
Concatenating Rows
Often in database design we store different values in rows to take advantage of a normalized design. However many times we need to combine multiple rows of data into one row for a report of some sort. New author Carl P. Anderson brings us some interesting T-SQL code to accomplish this.
2011-03-04 (first published: 2009-10-14)
150,356 reads
SQL and the JOIN Operator
How the JOIN operator works, the different types of JOINs and relevant information about joining tables.
2011-03-03 (first published: 2009-10-07)
47,559 reads
Retrieve consecutive records from the table based the value difference
Retrieve consecutive records from the table based the value difference
2009-11-04 (first published: 2009-10-06)
940 reads
2009-10-02
4,632 reads
2009-10-21 (first published: 2009-10-01)
2,288 reads
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Question of the Day
Checking Identities
The DBCC CHECKIDENT command is used when working with identity values. I have a table with 10 rows in it that looks like this:
TravelLogID CityID StartDate EndDate 1 1 2025-01-11 2025-01-16 2 2 2025-01-11 2025-01-16 3 3 2025-01-11 2025-01-16 4 4 2025-01-11 2025-01-16 5 5 2025-01-11 2025-01-16 6 6 2025-01-11 2025-01-16 7 7 2025-01-11 2025-01-16 8 8 2025-01-11 2025-01-16 9 9 2025-01-11 2025-01-16 10 10 2025-01-11 2025-01-16The docs for DBCC CHECKIDENT say this if I run with only the table parameter: "If the current identity value for a table is less than the maximum identity value stored in the identity column, it is reset using the maximum value in the identity column. " I run this code:
DELETE dbo.TravelLog WHERE TravelLogID >= 9
GO
DBCC CHECKIDENT(TravelLog, RESEED)
GO
INSERT dbo.TravelLog
(
CityID,
StartDate,
EndDate
)
VALUES
(4, '2025-09-14', '2025-09-17')
GO
What is the identity value for the new row inserted by the insert statement above? See possible answers