>
> Well, if you’re going to apply SQL to JSON (say), then the first thing you
> have to do is define a mapping from JSON to tables. That’s not difficult to
> do.
>
> If by the “closure property” you want the result of any SQL query to be the
> representation of some JSON structure, then you’re not going to achieve that.
> That’s essentially the same as the update problem.
>
>
> So pretty much no subqueries (ok somebody is going to say that any query
> entailing a subquery can be rewritten without one) but AFAIC the language
> you are talking about isn't really SQL then.
I don’t follow. You can write any query you like; it’s just that the result is
a table that might not be mappable back to JSON.
>>
>
> So I'm SOL if it's a date then.
You won’t get any dates in the table representation of JSON, but you can get
them in tables returned by a query.
>
>>
>
> Forgive me if I'm wrong. But I still don't believe I can write a statement
> that gets me the 5th row of the table.
Well, a typical representation of a JSON array [“a”, “b”, “c”] might be the
table
ARRAYS
ID INDEX TYPE VALUE
001 0 String “a”
001 1 String “b”
001 2 String “c”
and the query to get item 2 of array 001 would be
SELECT TYPE, VALUE FROM ARRAYS WHERE ID=001 AND INDEX=2
As far as I understand it this is similar to the mapping that SQL Server uses
for XML.
>
>
> How would you predict a priori what your table and column names would be and
> how many of them.
If you’ve got no schema then you have to use a generic mapping in which the
table and column names are generic concepts such as ARRAY, MAP, etc.
>
>
> If you don't can't predict the schema your semi-structured is going to
> generate then how could you write your query.
With difficulty. I can’t see anyone wanting to write it by hand.
Michael Kay
Saxonica
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