Fix to #28881 - Consider removing unnecessary CASTs around JSON_VALUE

[maumar]

We can remove cast for string scalars, other types maybe cause conversion issues in the generated sql.

Fixes #28881

[ghost]

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[roji]

Great to see this.

IMHO we should consider patching this... it certainly seems low-risk, and this issue prevents indexing from being used on strings properties in JSON, as we've seen in the recent conversations on Twitter.

[maumar]

@ajcvickers to make the call if we should patch. Risk does seem low.

[roji]

@maumar let me know when you want a review on this.

[maumar]

@roji ready for the review

[roji]

LGTM @maumar, but one question - this removes the cast also for cases where we have a length (e.g. nvarchar(10)).

I think it's a bit dubious to have this kind of type mapping on a JSON property, since it's not supported by the database in any way: JSON properties don't have types like columns, and the database never enforces a max length on them, etc.

But regardless... We can leave the cast, in order to have the DB truncate the string (in case someone inserted a longer value into the database). I don't think it's important to do that, mostly raising it as a question.