获取丢失数

Question

可能重复：
Find the smallest unused number in SQL Server

我有这样的表在SQL Server

ID | LetterID | LetterName 

ID => int和身份

LetterID => int和独特和从我的C＃应用​​程序和用户设置数NOTNULL

LetterName =>串

LetterID填充为it.for例如1,2,3,4,5 ,. ..，100，..（每行增加一个单位）现在我的LetterID是100但有时用户从表中删除一行，例如删除行，其中LetterID是50，现在用于插入新行（在应用程序中）我建议他LetterID选择50，我如何从表格中找到缺失的数字？

Answer 1

得到一个空白/缺失的行

SELECT TOP 1 x.LetterID +1 
FROM tablename x 
WHERE NOT EXISTS(SELECT * FROM tablename xx WHERE xx.LetterID = x.LetterID + 1) 
ORDER BY x.LetterID 

Answer 2

select t1.ID, t1.LetterID-1 
from yourtable t1 
    left join yourtable t2 
on t1.LetterID = t2.LetterID+1 
and t1.ID = t2.ID 
where t2.ID is null 
and t1.LetterID>(select MIN(LetterID) from yourtable where ID = t1.ID) 

Answer 3

var output = Enumerable.Range(1, list.Max(item => item.LetterID)) 
      .Except(list.Select(item => item.LetterID)) 

Answer 4

​​