Search With LIKE inside a JSON object in Mysql [duplicate] - mysql

Question

I have a MySQL query, where I filter by a json field:
SELECT id, username
FROM (SELECT id,
Json_extract(payload, '$.username') AS username
FROM table1) AS tmp
WHERE username = 'userName1';
It returns 1 row, which looks like:
1, "userName1" See the quotes that are not in the clause?
What I need is to make the WHERE clause case insensitive.
But when I do
WHERE username LIKE 'userName1';
it returns 0 rows. I don't understand why it works this way, the = clause works though it doesn't have those double quotes.
If I do
WHERE username LIKE '%userName1%';
now also returns the row, because %% takes quotes into consideration:
1, "userName1"
But when I do
WHERE username LIKE '%username1%';
it returns 0 rows, so unlike the usual MySQL LIKE it's somehow case sensitive.
What am I doing wrong and how to filter the json payload the case insensitive way?
EDIT=========================================
The guess is that COLLATE should be used here, but so far I don't understand how to make it work.

Answer 1

Default collation of MySQL is latin1_swedish_ci before 8.0 and utf8mb4_0900_ai_ci since 8.0. So non-binary string comparisons are case-insensitive by default in ordinary columns.
However, as mentioned in MySQL manual for JSON type
MySQL handles strings used in JSON context using the utf8mb4 character set and utf8mb4_bin collation.".
Therefore, your JSON value is in utf8mb4_bin collation and you need to apply a case insensitive collation to either operand to make the comparison case insensitive.
E.g.
WHERE username COLLATE XXX LIKE '...'
where XXX should be a utf8mb4 collation (such as the utf8mb4_general_ci you've mentioned.).
Or
WHERE username LIKE '...' COLLATE YYY
where YYY should be a collation that match the character set of you connection.
For equality comparison, you should unquote the JSON value with JSON_UNQUOTE() or the unquoting extraction operator ->>
E.g.
JSON_UNQUOTE(JSON_EXTRACT(payload, '$.username'))
Or simply
payload->>'$.username'
The JSON type and functions work way different from ordinary data types. It appears that you are new to it. So I would suggest you to read the manual carefully before putting it into a production environment.

Answer 2

Okay, I was able to solve the case insensitivity by adding COLLATE utf8mb4_general_ci after the LIKE clause.
So the point here is to find a working collation, which in its turn can be found by researching the db you work with.