How to replace JSON key's value in mysql - mysql

Question

I have a mysql JSON column like:
column value
data [{ "report1": { "result": "5"}, "report2": {"result": "6"}, "report3": {"a": "4"}}, {"report1": { "result": "9"},"report4": {"details": "<b>We need to show the details here</b>"}, "report3": {"result": "5"}}]
another instance of data is:
[{ "report1": { "result": "5"}, "report2": {"result": "6"}, "report3": {"a": "4"}}, {"report1": { "result": "9"}, "report3": {"result": "5"},"report4": {"details": "<b>We need to show the details here</b>"}}]
In above record the key is present on 2nd index.
And in this:
[{ "report1": { "result": "5"}, "report2": {"result": "6"}, "report3": {"a": "4"}}, {"report1": { "result": "9"}, "report3": {"result": "5"}}]
The key is not present.
I need to replace {"details": "<b>We need to show the details here</b>"}, i.e. key report4's value with just [], I need now data in this report.
Actually, the logic for generating data have been changed from XML data to JSON for only that key, so, we need to replace it with a blank array, the target type now, without affecting the other data.
Is there any direct solution to that? I'm avoiding creating procedures here.
So, The Target data will be:
[{ "report1": { "result": "5"}, "report2": {"result": "6"}, "report3": {"a": "4"}}, {"report1": { "result": "9"},"report4": [], "report3": {"result": "5"}}]
And yes the keys in JSON are not consistent, means, a key may present in next or previous record in the table but may not present in this record.

Answer 1

The column should be of type JSON to use MySQL's JSON features efficiently. Then use the JSON modification functions, such as JSON_REPLACE.
Since each value contains a JSON array whose size may not be known in advance, you can create a small utility function to modify each element in the array.
create function modify_json(val json)
returns json
deterministic
begin
declare len int default json_length(val);
declare i int default 0;
while i < len do
# Replace the report4 property of the i'th element with an empty list
set val = json_replace(val, concat('$[', i, '].report4'), '[]');
set i = i + 1;
end while;
return val;
end;
With your utility function, update the records:
update table set data = modify_json(data)
where json_contains_path(data, 'one', '$[*].report4');
The records containing at least one element with a report4 property will be updated according to the modify_json function in this case. You could achieve the same thing with multiple update commands that operate on each index of the JSON array separately.
If the column can't be of type JSON for some reason, then you can allow MySQL to coerce the data or your program can marshall the string into a JSON object, modify the data, then serialize it to a string, and update the row.