在 SQL 中查找序列的空缺而不创建额外的表

Question

我有一个 table invoices 字段 invoice_number。这是我执行 select invoice_number from invoice:

时发生的情况

invoice_number
--------------
1
2
3
5
6
10
11

我想要一个 SQL 给我以下结果：

gap_start | gap_end
4         | 4
7         | 9

如何编写 SQL 来执行此类查询？我正在使用 PostgreSQL.

Answer 1

与modern SQL, this can easily be done using window functions:

select invoice_number + 1 as gap_start, 
       next_nr - 1 as gap_end
from (
  select invoice_number, 
         lead(invoice_number) over (order by invoice_number) as next_nr
  from invoices
) nr
where invoice_number + 1 <> next_nr;

SQLFiddle: http://sqlfiddle.com/#!15/1e807/1

Answer 2

我找到了另一个查询：

 select invoice_number + lag gap_start, 
        invoice_number + lead - 1 gap_end
    from (select invoice_number, 
                 invoice_number - lag(invoice_number) over w lag,
                 lead(invoice_number) over w - invoice_number lead 
              from invoices window w as (order by invoice_number)) x 
  where lag = 1 and lead > 1;

Answer 3

我们可以使用一种更简单的技术首先获取所有缺失值，方法是连接生成的序列列，如下所示：

select series
from generate_series(1, 11, 1) series
left join invoices on series = invoices.invoice_number
where invoice_number is null;

这为我们提供了一系列缺失数字，在某些情况下它本身就很有用。

要获得间隙 start/end 范围，我们可以改为将源 table 与其自身连接。

select invoices.invoice_number + 1 as start, 
       min(fr.invoice_number) - 1 as stop
from invoices
left join invoices r on invoices.invoice_number = r.invoice_number - 1
left join invoices fr on invoices.invoice_number < fr.invoice_number
where r.invoice_number is null
      and fr.invoice_number is not null
group by invoices.invoice_number,
         r.invoice_number;

dbfiddle: https://dbfiddle.uk/?rdbms=postgres_14&fiddle=32c5f3c021b0f1a876305a2bd3afafc9

这可能不如上述解决方案优化，但可能在 SQL 不支持 lead() 功能的服务器中有用。

全部归功于 SILOTA 文档中的这个优秀页面： http://www.silota.com/docs/recipes/sql-gap-analysis-missing-values-sequence.html

我强烈推荐阅读它，因为它逐步解释了解决方案。

在 SQL 中查找序列的空缺而不创建额外的表

Find gaps of a sequence in SQL without creating additional tables

sql

postgresql

gaps-and-islands