ISSUE-4558: Add check_json function

[kevinw66]

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Summary

Add check_json function

Changelog

• New Feature

Related Issues

Fixes #4558

Test Plan

Unit Tests

Stateless Tests

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[mergify]

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[kevinw66]

@b41sh I don't know if the testcase for NullColumn is correct or not, please help review it

[kevinw66]

Still has some problem, Please wait

[kevinw66]

Still has some problem, Please wait

The console output for null has different case.

mysql> select check_json('123.12');
+----------------------+
| check_json('123.12') |
+----------------------+
| null                 |
+----------------------+

mysql> select check_json(v), v from t1;
+---------------+-----------+
| check_json(v) | v         |
+---------------+-----------+
| NULL          | NULL      |
| NULL          | null      |
| NULL          | true      |
| NULL          | 123       |
| NULL          | "abc"     |
| NULL          | [1,2,3]   |
| NULL          | {"a":"b"} |
+---------------+-----------+

[b41sh]

Still has some problem, Please wait

The console output for null has different case.

mysql> select check_json('123.12');
+----------------------+
| check_json('123.12') |
+----------------------+
| null                 |
+----------------------+

mysql> select check_json(v), v from t1;
+---------------+-----------+
| check_json(v) | v         |
+---------------+-----------+
| NULL          | NULL      |
| NULL          | null      |
| NULL          | true      |
| NULL          | 123       |
| NULL          | "abc"     |
| NULL          | [1,2,3]   |
| NULL          | {"a":"b"} |
+---------------+-----------+

@kevinw66 select check_json('123.12'); return null is because you check is_nullable() and return a no nullable column, so we can't get a NULL value. Modify function return_type to always return nullable column.

[b41sh]

/LGTM