MDEV-40972 JSON_TABLE's ON ERROR / ON EMPTY / DEFAULT Clauses Are All Silently Ignored

[DerZc]

JSON_TABLE can return a converted zero for a nonnumeric JSON string even when the column specifies NULL ON ERROR. For example, converting the value in {"a":"str"} to an INT column should take the column's error response and return NULL.

Bug report: https://jira.mariadb.org/browse/MDEV-40972

Root cause

The scalar conversion helper discards Field::store()'s return value. A shared Counting_error_handler also fails to represent conversion warnings as a column-local conversion failure. As a result, the provisional converted value can be returned without invoking the column's ON ERROR response.

Changes

• Return the scalar field-store status through an output argument.
• Use a conversion-local error handler to capture warnings and errors while leaving notes visible.
• Combine the store status and captured conversion failure before invoking the existing ON ERROR responder.
• Scope the JSON-format counting handler to its individual conversion so diagnostics from one column do not become another column's conversion state.

Regression coverage

The regression converts a nonnumeric JSON string to INT with NULL ON ERROR and expects SQL NULL. The implementation uses the existing error responder for NULL, DEFAULT, and ERROR policies; the regression directly covers the NULL policy.

• mysql-test/main/json_table_null_on_error.result
• mysql-test/main/json_table_null_on_error.test

Validation

On 11.4 at d10e5d726799b1cd57cc866f40aad68c720803da:

• The server build passed.
• main.json_table_null_on_error failed on the unchanged target branch and passed with this fix.
• Existing MTR tests passed: main.func_json, main.select, main.type_decimal, main.type_float.
• MTR reported no test-state cleanup failures.
• The full regression suite was not run.

[CLAassistant]

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