Improving Performance For JSON In SQL Server

Bert Wagner shows how to use indexed, non-persisted columns to pre-parse JSON data in SQL Server:

This is basically a cheat code for indexing computed columns.

SQL will only compute the “Make” value on a row’s insert or update into the table (or during the initial index creation) — all future retrievals of our computed column will come from the pre-computed index page.

This is how SQL is able to parse indexed JSON properties so fast; instead of needing to do a table scan and parsing the JSON data for each row of our table, SQL Server can go look up the pre-parsed values in the index and return the correct data incredibly fast.

Personally, I think this makes JSON that much easier (and practical) to use in SQL Server 2016. Even though we are storing large JSON strings in our database, we can still index individual properties and return results incredibly fast.

It’s great that the database engine is smart enough to do this, but I’m not really a big fan of storing data in JSON and parsing it within SQL Server, as that violates first normal form.  If you know you’re going to use Make as an attribute and query it in SQL, make it a real attribute instead of holding multiple values in a single attribute.

JSON Dates In SQL Server

Bert Wagner explains how to handle JSON datetime strings in SQL Server:

In SQL Server, datetime2’s format is defined as follows:

YYYY-MM-DD hh:mm:ss[.fractional seconds]

JSON date time strings are defined like:

YYYY-MM-DDTHH:mm:ss.sssZ

Honestly, they look pretty similar. However, there are few key differences:

  • JSON separates the date and time portion of the string with the letter T

  • The Z is optional and indicates that the datetime is in UTC (if the Z is left off, JavaScript defaults to UTC). You can also specify a different timezone by replacing the Z with a + or  along with HH:mm (ie. -05:00 for Eastern Standard Time)

  • The precision of SQL’s datetime2 goes out to 7 decimal places, in JSON and JavaScript it only goes out to 3 places, so truncation may occur.

Read on for a few scripts handling datetime conversions between these types.

When To Store JSON In SQL Server

Kevin Feasel

2017-03-15

JSON

Bert Wagner thinks about which conditions should hold for it to make sense to store JSON in SQL Server:

Every once in a while I hear of some technologist say that relational databases are dead; instead, a non-table based NoSQL storage format is the way of the future. SQL Server 2016 introduced JSON functionality, making it possible for some “non-SQL” data storage to make its way into the traditionally tabled-based SQL Server.

Does this mean all data in SQL Server going forward should be stored in long JSON strings? No, that would be a terrible idea. There are instances when storing JSON in SQL Server is a good choice though. In this post I want to create recommendations for when data should be stored as JSON and when it shouldn’t.

Protip:  anyone who says relational databases are dead is already working with one strike against.  Bert has great use cases for JSON as well as a good understanding that there are plenty of anti-use cases, making his post well worth reading.

Parsing Gigantic JSON Text

Kevin Feasel

2017-02-20

JSON

Jovan Popvic has created a 4.35 GB JSON array:

SQL Server 2016 and Azure SQL Database enable you to parse JSON text and transform it into tabular format. In this post, you might see that JSON functions can handle very large JSON text – up to 4GB.

First, I would need very large JSON document. I’m using TPCH database so I will export the content of lineitem table in a file. JSON can be exported using the bcp.exe program:

My first draft read “Jovan Popovic has created a monster.”  I might go back to that one.  On the plus side, the operation took a lot less time than I had expected, though I’d have to imagine that his SQL Express instance had some decent specs.

High-Compression JSON With vNext

Jovan Popovic gives an example of 25x compression of JSON data using a clustered columnstore index in vNext:

CLUSTERED COLUMNSTORE INDEXES provide extreme data compression in SQL Server and Azure SQL Database. With NVARCHAR(MAX) support in CCI indexes you can use them on your JSON data stored is database and get high 25x compression. Therefore, CCI is a perfect solution if you need to store a large volume of JSON data in your SQL Database.

ContosoDW database is publicly available for download, so you can use this database and the script below to re-create this table and try this in your environment.

I’m curious whether this will also apply to non-JSON data.

BCP Output In JSON Line-Delimited Format

Kevin Feasel

2017-02-09

JSON

Jovan Popovic shows how to use FOR JSON PATH to output rows in a table to JSON line-delimited format:

Although this is not a valid JSON format, many system use it to exchange data.

One advantage of line-delimited JSON format compared to the standard JSON is the fact that you can append new JSON objects at the end of the file without removing closing array bracket as in the standard JSON.

This might be a niche use case, but I’m sure that in this post-XML-all-the-things era, this is more common than you might first expect.

JSON In Clustered Columnstore Indexes

Jovan Popovic gives a use case for JSON data being part of a clustered columnstore index:

This is equivalent to collections that you might find in classic NoSQL database because they store each JSON document as a single entity and optionally create indexes on these documents. The only difference is CLUSTERED COLUMNSTORE index on this table that provides the following benefits:

  1. Data compression – CCI uses various techniques to analyze your data and choose optimal compression algorithms to compress data.

  2. Batch mode analytic – queries executed on CCI process rows in the batches from 100 to 900 rows, which might be much faster than row-mode execution.

I think it’s worth reading this in conjunction with Niko Neugebauer’s comments regarding strings in columnstore.

JSON Basics In SQL Server

Kevin Feasel

2017-01-25

JSON, T-SQL

Neil Gelder gives an introduction to JSON in SQL Server 2016:

A new feature in SQL Server 2016 (also available in Azure SQL database) is the ability to create and query  JSON (Javascript object notation) documents, which have now become a common alternative to XML.

Lets look at some examples, I’ll be using tables from the new sample database for SQL Server 2016 WorldWideImporters which you can download from this link

I’m of two minds with JSON support:  I think it’s very useful for building output sets for service calls and might be fine for inputs when you can’t use a table-valued parameter for some reason, but if you’re doing a lot of JSON splitting of data in a table, that’s a violation of first normal form.

Parsing JSON In R

Kevin Feasel

2017-01-10

JSON, R, T-SQL

Tomaz Kastrun shows how to feed a JSON data set into R and turn that into a proper data frame:

JSON has very powerful statements for converting to and from JSON for storing into / from SQL Server engine (FOR JSON and JSON VALUE, etc).  And since it is gaining popularity for data exchange, I was curious to give it a try with R combination.

I will simply convert a system table into array using for json clause.

There’s an R library.  There’s always an R library.

Generating JSON In Power BI

Chris Webb shows how to generate JSON in M:

Often, when calling web services from Power BI or Power Query, you’ll need to generate some JSON inside your query to send to these web services. The M language makes this relatively easy to do with the Json.FromValue() function but there’s only one example of how to use it in the help so I though it might be useful to provide some worked examples of M data types and how Json.FromValue() turns them into JSON.

First, here’s a function – that I’ve called GetJson() for the examples here – that takes a parameter of any data type, passes it to Json.FromValue() and returns the JSON representation of the input as text:

Read on for the code sample.

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