1. A JSON’s Journey through SQL Server
Shamil Sadique (MCSE, OCA)
Senior DBA – Pearson Lanka (Pvt) Ltd.
@shamilsaleem
A JSON’s Journey through SQL Server

2. JSON Overview

3. What is JSON
JavaScript Object Notation (JSON) an open standard format for data exchange between applications
Commonly used in web applications, and NoSQL datastores such as MongoDB and CouchDB
Language independent and flexible, hence have become popular in the industry

4. The JSON Object Consists of key-value pairs Values separated by comma
Values can be
String
Number
True/false
Objects (arrays / nested json objects)

6. Road to JSON Support in SQL Server
Feature was Requested to Microsoft Connect by the community in 2011
Was one of the most popular feature request until it was implemented

8. JSON Prior to SQL Server 2016
CLR-based solutions
DLL libraries to extend support into reading JSON data.
TSQL-based solutions
UDFs written to decode JSON data.
Both being External Tools and Approaches

9. Native JSON Support

10. Storing JSON in SQL Server
Native support introduced in SQL Server 2016
No special JSON datatype, but uses “nvarchar” due to :
Backward compatibility
Enable old applications/codebase to integrate with this feature
Cross feature compatibility
Get the support of all sql server features which are compatible with nvarchar. (memory-optimized tables, temporal tables, row level security)
Client side support
Client tools outside sql server represent JSON as string.

11. Disadvantages of not having a special datatype :
Performance could’ve been improved
Optimized index types would've been introduced.

12. Mapping between SQL server and JSON data types:
Category
SQL Data Type
JSON Data Type
Character
char, nchar
varchar, nvarchar
string
Numeric
int, bigint, float,
decimal numeric
number
Bit
bit
true/false
Date and Time
date, datetime, datetime2, time, datetimeoffset
Binary
binary
BASE64-encoded string
Other
uniqueidentifier, money

13. Native JSON Support Table data to JSON text JSON text to table data
Built in JSON functions

14. Business Case : “Smart University” Database

15. TABLE DATA TO JSON TEXT

16. FOR JSON FOR JSON AUTO PATH Automatically formats results into JSON
Nesting based on table hierarchy
Less control over the final result
Options Include :
ROOT
Creates a single root object
INCLUDE_NULL_VALUES
Don’t generate [] syntax
SQL Server normally adds [ ] assuming the query will return more than 1 row.
Full Control over the final results
Ability to nest / change the level of the resulting JSON

17. Demo : FOR JSON

18. Converting JSON text to table data

19. OPENJSON
Parses JSON text and returns the properties as rows and columns
Can be used in the FROM clause of a TSQL statement.
Available only under compatibility level 130 or higher

20. OPENJSON DEFAULT SCHEMA CUSTOMIZED SCHEMA
Always returns a resultset containing 3 columns.
The Columns can be customized
Additional “WITH” clause is used.

21. OPENJSON WTH DEFAULT SCHEMA
Only returns first level properties
Nested properties will be separate JSONs
A Resultset consists of 3 columns is returned.
Key
Name of the JSON property
Value
Value of the JSON property;
nulls are allowed on this column
datatype is nvarchar(max)
Type
The datatype of the value
Column only holds tinyint values
Value of the “Type” Column
Corresponding JSON Data Type
Null 1
String 2
Number 3
True/false 4
Array 5
Object

22. OPENJSON WITH CUSTOMIZED SCHEMA
Used to get a customized resultset with complex values.
Used the “WITH” clause in the OPENJSON function.
WITH clause maps the JSON attributes to the column names:
OPENJSON( jsonExpression [ , path ] ) [
WITH (
column_name data_type [ column_path ] [ AS JSON ]
[ , column_name data_type [ column_path ] [ AS JSON ] ]
[ , n ] ) ]

23. Demo : OPENJSON

24. Other uses of OPENJSON Transpose Comma Separated Values to a Column.
Compare data among rows.

25. Demo : Other Uses of OPENJSON

26. Extracting Specific Values

27. Extracting specific values form JSON
JSON_VALUE
Returns a scalar value from a JSON object.
JSON_QUERY
Returns an object or array value from a JSON object.

28. Demo : JSON_VALUE & JSON_QUERY

29. VALIDATING JSON DATA

30. isJSON Validates a JSON
Can be used in a check constraint validating a column which is supposed to insert JSON data.
No Native datatype for JSON, so this is important.

31. Demo : isJSON

32. PERFORMANCE CONSIDERATIONS

33. Indexing JSON Data Columns
Stored as text; no special datatype; hence no special indexes.
Ways to improve performance :
Create computer columns based on heavily using JSON tags and Index those Computed Columns
Utilize in full-text indexes
Hence, not recommended for large amounts of data.

34. Demo : Indexing Computed Columns

35. XML vs JSON in SQL Server
XML in SQL Server
JSON in SQL Server
Support introduced in SQL Server 2005
Introduced in SQL Server 2016
Has a dedicated datatype and indexes
No dedicated datatype, stored in nvarchar
Smaller footprint compared to the same data represented as JSON*
Larger footprint to save the same data compared to xml.
Automatically validates if inserted to a xml column*
No automatic validation as the datatype is plain nvarchar
XML Data retrieval is slower compared to JSON*
XMLDATA.VALUE, XMLDATA.QUERY
Data retrieval is faster
JSON_VALUE, JSON_QUERY *

36. QUESTIONS ?

37. Thank you !

38. References and Further Reading :
Stacia Varga, Denny Cherry, Joseph D’Antoni (2016). Introducing Microsoft SQL Server Mission-Critical Applications, Deeper Insights, Hyperscale Cloud. Microsoft Press
William Durkin, Miloš Radivojević, Dejan Sarka (2017). SQL Server 2016 Developer's Guide. Packt Publishing