MDEV-28922 JSON_NORMALIZE handling of duplicate keys#5289
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This pull request adds test cases and a fix for handling duplicate keys in JSON_NORMALIZE (MDEV-28922). However, the implementation in strings/json_normalize.c contains a critical bug where it directly accesses the string member of the value union without checking its type, which can lead to undefined behavior, segmentation faults, or non-deterministic sorting. A recursive value comparison helper is recommended to safely compare different JSON types.
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Despite the JSON spec rfc8259/#section-4 "The names within an object SHOULD be unique"[1], it does happen. As our sort algorithm has access to both key and value, if the key matches, sort by the value. The type, and length of objects, strings, arrays and numbers is easy, so use those as a first comparision point. [1] https://www.rfc-editor.org/info/rfc8259/#section-4
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Despite the JSON spec rfc8259/#section-4
"The names within an object SHOULD be unique"[1], it does happen.
As our sort algorithm has access to both key and value, if the key matches, sort by the value.
[1] https://www.rfc-editor.org/info/rfc8259/#section-4