You can run SQL queries on individual JSON files... but you have to have PostgreSQL installed already.
And you can't run it against multiple JSON files, only one, with a single JSON object at the root.
You're right that you need to have Postgres installed. For running SQL over multiple JSON files, we wanted to keep the blog post short and noted several different ways to go over multiple files in our GitHub Readme.
1. You can create a partitioned PostgreSQL table, and declare one child table per JSON file. You can also declare constraints on the child table to filter out irrelevant files to the query.
2. You can create a distributed foreign table on CitusDB, even if you'd like to run on one node. In this case, we'll collect statistics automatically for you, and filter out irrelevant files.
3. If neither of these fit, you could change the source code to scan over one directory instead of a file. We didn't go down this path to be compatible with file_fdw's semantics.
That is:
- you can take heterogenous JSON documents, and then make them appear to the Postgres world as separate tables. (Which they have to be, because they're not uniform)
- you can then take some kinds of SQL queries and distribute them among these tables, as if they were one big SQL table. If some pseudo-tables have missing or extra columns, no problem.
You could in fact have heterogeneous JSON documents within one file, and json_fdw could still handle them. If a field you declared in the table schema doesn't appear in a JSON document, json_fdw would just consider that field to be Null.
The issue is, json_fdw is built such that one table can only associated with one JSON file, and users typically have many JSON files lying around. For example, you'd have one JSON file for each hour's worth of website error logs.
If that's the case, you could create a distributed table. That way, you could run the query one distributed table and have the query run on all your JSON files instead of just one.
That said, it's probably best to associate one type of JSON logs (say your website error logs) with one distributed table. That way, your queries go over your website error logs or your mobile application logs, but not both at the same time.
In the file system, to prevent too many records in a single directory it was split up per 1000 records... base/00001000/(1000-1999).json.gz ... this was mainly for being able to navigate this structure via a gui. I would suggest if your system can't do "basepath//*.json.gz" that you consider it.
A good use case is exploring external APIs, many of which come back as JSON. This might be a faster awy to figure out what you're dealing with: how large, how many, unique values, mins, maxes, etc. It could be especially useful if you need to match it to existing keys or metadata that you already have in the same database. To solve this same problem before, I've written lots of one-off scripts that convert the JSON into a CSV so that I can view it in Excel. This may or may not help me there, but good to see another tool.
It's important for these files to be kept this way, because they can be submitted to a SCM (perforce, svn, etc.), and this is the typical workflow. An SQL/noSQL db won't cut it here, since there is no revision number, or even if there is, it introduces a problem of syncing what's in the DB vs. what's in SCM.
So such tool would become interresting, if after syncing your latest data of the depot (repo), you run a tool that imports them into the DB to be used by other tools. And when you are done, export is done to the same files, and submitted.
Some automation could be done as well.
And having such tools would be beneficial, since you now don't have to write another tool to be ran manually, or being resident as service to get the latest file changes and update the DB, but could be make as an PostgreSQL worker that imports on the fly changes and updates the DB at the same time.
E.g. - if you use Perforce: - Someone syncs - The DB automatically picks up the changes, informed by the file system, and updates the DB.
The more of such things the better.