Question

使用MySQL，我如何最好地查询~100,000行的表，以在序列号的型号中查找缺失值。例如，在时钟收音机（下面的型号＃123）和计算器（下面的型号＃345）中找到丢失的序列号。

数据如下所示：

MODEL＃，SERIAL＃

123,1 123,2 123,4 123,5 345,101
345,104
345,105
345,106

所需的输出将是

MODEL＃，SERIAL＃

123,3 345,102
345,103

请注意，每个型号的序列号都有不同的起始值。

谢谢！

Answer 1

很难找到那些缺失的东西。弥补差距要容易得多。因此，这将返回第一个缺失的序列和缺少的数字：

select t.serial + 1 as FirstMissing,
       (t.next_serial - t.serial) - 1 as numMissing
from (select t.*,
             (select t2.serial
              from data t2
              where t2.model = t.model and t2.serial > t.serial
              order by t2.serial asc
              limit 1
             ) as next_serial
      from data t
     ) t
where next_serial <> serial + 1;

Answer 2

要确定该表中不存在某些内容，您可以LEFT JOIN到该表并测试结果IS NULL。例如，给定任何（模型，序列）对，您可以构造期望遵循给定的一对的（模型，序列）对。这是相同的型号，序号为1。然后LEFT JOIN表自身，条件是（模型，序列）对等于预期的一对。对于任何缺失的序列号，自联接别名IS NULL中的每一列，请添加WHERE条件，仅保留这些行。

以下内容将帮助您入门。它标识了每个间隙的 start ，但不是间隙中的所有数字。

-- List all rows in table serials
-- 1. which aren't the highest for a given SKU, and
-- 2. for which the following serial number doesn't exist for the same SKU
SELECT ser1.sku, ser1.serial_num + 1 AS serial_num
FROM serials AS ser1
INNER JOIN (
  SELECT sku, MAX(serial_num) AS serial_num
  FROM serials
  GROUP BY sku
) AS sermax
ON (ser1.sku = sermax.sku
    AND ser1.serial_num < sermax.serial_num)
LEFT JOIN serials AS ser2
ON (ser1.sku = ser2.sku
    AND ser1.serial_num + 1 = ser2.serial_num)
WHERE ser2.serial_num IS NULL

输出：

sku|serial_num
123|        3
345|      102

_{此答案中的代码为双重许可：CC BY-SA 3.0或MIT License as published by OSI。}

查找MySQL

2 个答案: