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Category: JSON

JSON Leads To New Wave Of 1NF Failures

Jovan Popovic talks about storing JSON in SQL Server:

Instead of single JSON object you can organize your data in this “collection”. If you do not want to explicitly check structure of each JSON column, you don’t need to add JSON check constraint on every column (in this example I have added CHECK constraint only on EmailAddresses column).

If you compare this structure to the standard NoSQL collection, you might notice that you will have faster access to strongly typed data (FirstName and LastName). Therefore, this solution is good choice for hybrid models where you can identify some information that are repeated across all objects, and other variable information can be stored as JSON. This way, you can combine flexibility and performance.

Okay, we’ve hit my first major problem with JSON support:  rampant violation of first normal form.  You can create check constraints on JSON code, and that’s pretty snazzy I guess, but I know a better way to store relational data in a relational database system.  JSON support is great when you ask SQL Server to be a holder of text blobs, but this is begging for bad design decisions.

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JSON In SQL 2016

Jovan Popovic has a couple of posts on JSON.  First, using OPENJSON to generate a tally table:

Problem: I want to dynamically generate a table of numbers (e.g. from 0 to N). Unfortunately we don’t have this kind of function in SQL Server 2016, but we can use OPENJSON as a workaround.

OPENJSON can parse array of numbers [1,25,3,5,32334,54,24,3] and return a table with [key,value] pairs. Values will be elements of the array, and keys will be indexes (e.g. numbers from 0  to length of array – 1). In this example I don’t care about values I just need indexes.

Well, that’s one way to do it.

Also, Jovan talks about performance of FOR JSON PATH:

You might notice that table scans take majority of the query cost. Cost of the FOR JSON (JSON SELECT operator) is 0% compared to others. Also, since we are joining small tables (one sales order and few details), cost of the JOIN is minor. Therefore, if you processing small requests there will be no performance difference between formatting JSON on client side and in database layer.

This comment was actually due to a bug in the AdventureWorks CTP 3 database.  The good news is that JSON isn’t obviously slow performance problems, but I’d like to see some more thorough performance tests.

Both posts via Database Weekly.

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