How Can I Find Missing IDs in a MySQL Table?

Identifying Missing Identifiers in a MySQL Table

Within a MySQL table, it's possible to encounter missing identifiers, creating gaps in the numerical sequence. To retrieve these missing IDs, a specific query is required.

Query for Missing IDs

Consider the example table provided:

ID	Name
1	Bob
4	Adam
6	Someguy

From this table, it's evident that the IDs 2, 3, and 5 are missing. To extract these missing identifiers, the following query can be employed:

SELECT a.id+1 AS start, MIN(b.id) - 1 AS end
FROM testtable AS a, testtable AS b
WHERE a.id < b.id
GROUP BY a.id
HAVING start < MIN(b.id);

Explanation

• The testtable is self-joined to compare adjacent rows.
• The id 1 (start) represents the potential missing ID immediately following the current ID (a.id).
• The MIN(b.id) - 1 (end) represents the difference between the minimum ID greater than the start value and 1, indicating the potential end of the missing ID range.
• The rows satisfying the condition start < MIN(b.id) are the ranges with missing IDs.

Additional Resources

For further insight on this topic, refer to the following:

• [Example Sequence Gap Code](https://web.archive.org/web/20220706195255/http://www.codediesel.com/mysql/sequence-gaps-in-mysql/)

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