已用编号分布查询

--测试数据
CREATE TABLE tb(col1 varchar(10),col2 int)
INSERT tb SELECT 'a',2
UNION ALL SELECT 'a',3
UNION ALL SELECT 'a',6
UNION ALL SELECT 'a',7
UNION ALL SELECT 'a',8
UNION ALL SELECT 'b',3
UNION ALL SELECT 'b',5
UNION ALL SELECT 'b',6
UNION ALL SELECT 'b',7
GO

--已用编号分布查询
SELECT id=IDENTITY(int),col1,col2 INTO #1 FROM tb a
WHERE NOT EXISTS(
    SELECT * FROM tb WHERE col1=a.col1 AND col2=a.col2-1)
SELECT id=IDENTITY(int),col2 INTO #2 FROM tb a
WHERE NOT EXISTS(
    SELECT * FROM tb WHERE col1=a.col1 AND col2=a.col2+1)
SELECT a.col1,start_col2=a.col2,end_col2=b.col2
FROM #1 a,#2 b
WHERE a.id=b.id
DROP TABLE #1,#2
/*--结果
col1       start_col2  end_col2    
-------------- -------------- -----------
a          2           3
a          6           8
b          3           3
b          5           7
--*/