How can I check a group of numbers are consecutive in T-SQL?

Question

If i was to have a table with an integer column containing n number of rows and wanted to check if they were consecutive, how could I do this?

DECLA         


        

Answer 1

Solution 1: (I have assumed the next value is current value plus 1; also I have added a PK):

DECLARE @Temp TABLE 
(
    IntegerValue INT PRIMARY KEY,
    Processed BIT
);

INSERT  @Temp(IntegerValue)
SELECT  1
UNION ALL
SELECT  2
UNION ALL
SELECT  3
UNION ALL
SELECT  4
UNION ALL
SELECT  5;

--Test 1
DECLARE @RowCount INT;
SELECT  @RowCount=COUNT(*)
FROM    @Temp a
LEFT JOIN @Temp b ON a.IntegerValue+1=b.IntegerValue
WHERE   b.IntegerValue IS NOT NULL
OR      b.IntegerValue IS NULL
AND     a.IntegerValue = (SELECT MAX(IntegerValue) FROM @Temp);

IF @RowCount = (SELECT COUNT(*) FROM @Temp)
    SELECT 'CONSECUTIVE' Test1_Result
ELSE
    SELECT 'not CONSECUTIVE' Test1_Result;

--Test 2
DELETE @Temp;
INSERT  @Temp(IntegerValue)
SELECT  1
UNION ALL
SELECT  2
UNION ALL
SELECT  3
UNION ALL
SELECT  400
UNION ALL
SELECT  5;

SELECT  @RowCount=COUNT(*)
FROM    @Temp a
LEFT JOIN @Temp b ON a.IntegerValue+1=b.IntegerValue
WHERE   b.IntegerValue IS NOT NULL
OR      b.IntegerValue IS NULL
AND     a.IntegerValue = (SELECT MAX(IntegerValue) FROM @Temp);

IF @RowCount = (SELECT COUNT(*) FROM @Temp)
    SELECT 'CONSECUTIVE' Test2_Result
ELSE
    SELECT 'not CONSECUTIVE' Test2_Result;

Solution 2: (less logical reads; the minimum IntegerValue must be 1)

DECLARE @Temp TABLE 
(
    IntegerValue INT PRIMARY KEY,
    Processed BIT
);

INSERT  @Temp(IntegerValue)
SELECT  v.number
FROM    master.dbo.spt_values v
WHERE   v.type = 'P'
AND     v.number > 0;

SELECT CASE WHEN 
    (
        SELECT  TOP 1 q.IntegerValue
        FROM
        (
            SELECT  a.IntegerValue
                    ,ROW_NUMBER() OVER(ORDER BY a.IntegerValue) Num
            FROM    @Temp a
        ) q
        WHERE   q.IntegerValue <> q.Num
    ) IS NULL THEN 'Y' ELSE 'N' END

Solution 3: ("quirky select" method; less logical reads, lower elapsed time)

DECLARE @Temp TABLE 
(
    IntegerValue INT PRIMARY KEY,
    Processed BIT
);

INSERT  @Temp(IntegerValue)
SELECT  1
UNION ALL
SELECT  2
UNION ALL
SELECT  3
UNION ALL
SELECT  4
UNION ALL
SELECT  5;

DECLARE @IsConsecutive BIT,
    @PreviousIntegerValue INT;

SELECT  @IsConsecutive = 1;

SELECT   @IsConsecutive = CASE WHEN @PreviousIntegerValue + 1 <> a.IntegerValue /*AND a.IntegerValue IS NOT NULL = condition necessary if IntegerValue field allows NULLs */ THEN 0 ELSE @IsConsecutive END
        ,@PreviousIntegerValue = a.IntegerValue
FROM    @Temp a
ORDER BY a.IntegerValue ASC
OPTION (MAXDOP 1);

SELECT  @IsConsecutive [IsConsecutive];