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UPDATE with ORDER BY

The statement succeeds if it updates id values first by setting 2 to 1 and then 3 to 2. However, it fails if it first tries to set 3 to 2. That would result in two records having an id value of 2, so a duplicate-key violation occurs. To solve this problem, add an ORDER BY clause to cause the row updates to occur in a particular order:

UPDATE people SET id=id-1 ORDER BY id;

Row contents will be as follows;

+-------------------+
| id | name | age |
+-------------------+
| 1 | Victor | 21 |
| 2 | Susan | 15 |
+-------------------+
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