How to get first gap in a column containing sequential int values

问题

I have a column in a SQL Server database table, there is a column containing integer values and I would like to get the max value unless there is a gap in the series, then I would like to get the first missing value.

For example from the below table, I am looking to get value 4

1
2
null
3

The above is simple, however if the table contains data like below, how can I find which id I am missing, in this case it would be 8

1
3
2
4
null
5
7
6
null
10
9

//////////////////

Edit:

I Initially implemented @podiluska's answer and was going to accept it however when I tested with a table with over 10K rows it was quite slow, so I have taken @vmvadivel's answer and changed it slightly as shown below and it works quite fast, but still not 100% what I wanted:

SELECT Number
FROM 
(
    SELECT ROW_NUMBER() OVER(ORDER BY iValue) AS Number
    FROM tblNumbers WHERE iValue IS NOT NULL
) temp
WHERE Number NOT IN 
(
    SELECT iValue FROM tblNumbers WHERE iValue IS NOT NULL
)

This works quite well however if all the iValue fields are null then I don't get anything back, but I want it to return 1 as it will be the first value in series, obviously I can handle this in the C# code but I am sure there must be a way of returning 1 if the above query does not return a row?

I have changed the top level Select Number with SELECT Coalesce(Number, 1) but it did not work, any ideas how to solve this?

Thanks

回答1:

If #t is your table

select min(t1.number)+1 
from #t t1
left join #t t2 
           on t1.number = t2.number-1
where t2.number is null

回答2:

If you have a number table which has sequential int value in it then you can do something like this:

SELECT * FROM 
(
    SELECT ROW_NUMBER() OVER(ORDER BY iValue) AS Number FROM tblNumbers
) temp
WHERE Number NOT IN 
(
    SELECT [ID] FROM tblFindGaps
)
GO

回答3:

SELECT
    t1.number + 1 AS range_start,
    MIN(t2.number) - 1 AS range_end
FROM test t1
INNER JOIN test t2
    ON t2.number > t1.number
WHERE t1.number IS NOT NULL
GROUP BY t1.number
HAVING t1.number + 1 <= MIN(t2.number) - 1

If you add a number 15 to the table, the output will be:

range_start  range_end
          8          8
         11         14

It finds each successive pair of numbers, with a gap of at least one. It then adds or subtracts one from this, so that the start_range and end_range is the range of the gap.

来源：https://stackoverflow.com/questions/11519630/how-to-get-first-gap-in-a-column-containing-sequential-int-values

标签

sql

sql-server

sql-server-2008-r2