Is there an opposite of MySQL's JSON_ARRAY_APPEND? - mysql

Question

I used UPDATE table SET col = JSON_ARRAY_APPEND(col, '$', 'BAZ') to add a value to my json column:
Before: ["FOO", "BAR"]
After: ["FOO", "BAR", "BAZ"]
How can I now remove the value, i.e. perform the reverse of JSON_ARRAY_APPEND? I've tried the following but it doesn't seem to pick up the value.
UPDATE table SET col = JSON_REMOVE(col, '$.BAZ')

Answer 1

You can remove array elements by position, not by value.
select json_remove('["FOO", "BAR", "BAZ"]', '$[2]') as array;
+----------------+
| array |
+----------------+
| ["FOO", "BAR"] |
+----------------+
But you can find the position with JSON_SEARCH():
select json_search('["FOO", "BAR", "BAZ"]', 'one', 'BAZ') as path;
+--------+
| path |
+--------+
| "$[2]" |
+--------+
You can see it strangely puts JSON double-quotes around that path. So you have to unquote it:
select json_unquote(json_search('["FOO", "BAR", "BAZ"]', 'one', 'BAZ')) as path;
+------+
| path |
+------+
| $[2] |
+------+
Then put it all together:
select json_remove('["FOO", "BAR", "BAZ"]', json_unquote(json_search('["FOO", "BAR", "BAZ"]', 'one', 'BAZ'))) as array;
+----------------+
| array |
+----------------+
| ["FOO", "BAR"] |
+----------------+
This would be a lot easier if you didn't use JSON arrays. Instead of using an array, put multi-valued attributes in a child table, with one value per row. Then you can delete using traditional SQL:
DELETE FROM child_table WHERE somvalue = 'BAZ';
I have answered a bunch of questions about using JSON in MySQL here on Stack Overflow, and I have yet to see an instance where using JSON is easier than using normalized tables.