

Ten Centuries
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Three answers:
1) I do not think that the documentation covers this topic very well, even though it is very intuitive. That is why I posted the question here.
2) Yes, 8 would have sufficed, but I set it to such a crazy large number to demonstrate a point. I always gets points better when they have crazy large numbers in them. :)
3) Yes, the temporary tables end when the session ends. I dropped them because of best practices/force of habit. It's like I tell my children, you have to put away your toys when you are done playing with them.




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Tricky. I had a 5050 chance and blew it!
Good question. Thanks.
Tom Garth Vertical Solutions
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SSCrazy
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I had some trouble understanding the explanation of the correct answer at first. The explanation for the answer states, "SQL Server will use the maximum identity value + increment in the direction of the increment for the next identity."
I'm not sure if there is any better way to word it. But I first thought "maximum identity value" was intended to mean 100 in example 2 (for example, SELECT MAX(Temp2ID) FROM #Temp2). Then I realized that the intended meaning was something like, "the value farthest in the direction of the increment value's sign." Or, in terms of SQL: MAX(ID) + 1 if the increment is >= 1, MIN(ID)  1, if the increment is <= 1.
Here is the sample code with two additional queries I wrote to help me understand it.
CREATE TABLE #Temp1 ( Temp1ID int NOT NULL IDENTITY (2147483648,1), Temp1Value char(1) NOT NULL ) ;
CREATE TABLE #Temp2 ( Temp2ID int NOT NULL IDENTITY (1,1), Temp2Value char(1) NOT NULL ) ;
INSERT INTO #Temp1 (Temp1Value) VALUES ('1') ; INSERT INTO #Temp1 (Temp1Value) VALUES ('2') ; SET IDENTITY_INSERT #Temp1 ON ; INSERT INTO #Temp1 (Temp1ID,Temp1Value) VALUES (100,'3') ; SET IDENTITY_INSERT #Temp1 OFF ;  Query to show current and next increment values. SELECT MAX(Temp1ID) AS CURRENT_INCREMENT_VALUE, MAX(Temp1ID) + 1 AS NEXT_INCREMENT_VALUE FROM #Temp1; INSERT INTO #Temp1 (Temp1Value) VALUES ('4') ;
INSERT INTO #Temp2 (Temp2Value) VALUES ('1') ; INSERT INTO #Temp2 (Temp2Value) VALUES ('2') ; SET IDENTITY_INSERT #Temp2 ON ; INSERT INTO #Temp2 (Temp2ID,Temp2Value) VALUES (100,'3') ;  Query to show current and next increment values.  Used adding a negative integer to demonstrate "increment" of 1. SELECT MIN(Temp2ID) AS CURRENT_INCREMENT_VALUE, MIN(Temp2ID) + (1) AS NEXT_INCREMENT_VALUE FROM #Temp2; SET IDENTITY_INSERT #Temp2 OFF ; INSERT INTO #Temp2 (Temp2Value) VALUES ('4') ;
SELECT Temp1ID,Temp2ID FROM #Temp1 t1 INNER JOIN #Temp2 t2 ON t1.Temp1Value = t2.Temp2Value WHERE t1.Temp1Value = '4' ;
DROP TABLE #Temp1 ; DROP TABLE #Temp2 ;
But it is good that SQL Server doesn't work in such a way as to make the wrong answer that I picked (101,99) correct. Otherwise, as others have noted, you would end up with ID collisions when using negative increments.
Thanks, webrunner
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SSCrazy
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Another great question, I had to think about this one, but it makes sense. Thanks!




SSCrazy
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I had to puzzle on this one for a while. Thanks.




SSC Rookie
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So, can we say that what SQL Server does to determine the next identity value is:
Select Sign(Ident_Incr('tablename')) * Max(Sign(Ident_Incr('tablename')) * $IDENTITY) + Ident_Incr('tablename') From tablename
where $IDENTITY is the identity column of table tablename ?




SSCEnthusiastic
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Hi,
i have trouble in understanding the solution. So as we have seen in the first table
CREATE TABLE #Temp1 ( Temp1ID int NOT NULL IDENTITY (2147483648,1), Temp1Value char(1) NOT NULL ) ;
INSERT INTO #Temp1 (Temp1Value) VALUES ('1') ; INSERT INTO #Temp1 (Temp1Value) VALUES ('2') ; SET IDENTITY_INSERT #Temp1 ON ; INSERT INTO #Temp1 (Temp1ID,Temp1Value) VALUES (100,'3') ; SET IDENTITY_INSERT #Temp1 OFF ; INSERT INTO #Temp1 (Temp1Value) VALUES ('4') ;
after we set identity insert off, the identity value start from 101 but similarly in the second table after identity insert off, still the next value is showing 3 not 101??
what is the difference in these two?
Thanks




SSCInsane
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BI_NewBie (1/9/2015) Hi,
i have trouble in understanding the solution. So as we have seen in the first table
CREATE TABLE #Temp1 ( Temp1ID int NOT NULL IDENTITY (2147483648,1), Temp1Value char(1) NOT NULL ) ;
INSERT INTO #Temp1 (Temp1Value) VALUES ('1') ; INSERT INTO #Temp1 (Temp1Value) VALUES ('2') ; SET IDENTITY_INSERT #Temp1 ON ; INSERT INTO #Temp1 (Temp1ID,Temp1Value) VALUES (100,'3') ; SET IDENTITY_INSERT #Temp1 OFF ; INSERT INTO #Temp1 (Temp1Value) VALUES ('4') ;
after we set identity insert off, the identity value start from 101 but similarly in the second table after identity insert off, still the next value is showing 3 not 101??
what is the difference in these two?
Thanks
In the second table the identity values are decreasing. This means the next value will be 3 since the identity value you inserted (100) is "less" than the next value to be inserted. I put less in quotes because we know 100 is not actually less than 3.
Lynn Pettis
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