SQL Server guide

Using JSON Array / Value functions

Below example shows how to select specific elements from value array or use JSON PATH expression to extract from document array

Standard SQL query example

This is the base query accepted by the connector. To execute it in SQL Server, you have to pass it to the Data Gateway via a Linked Server. See how to accomplish this using the examples below. 

SELECT _id
        , JSON_ARRAY_FIRST(colors) as first_color
        , JSON_ARRAY_LAST(colors) as last_color
        , JSON_ARRAY_NTH(colors,3) as third_color
        , JSON_VALUE(locationList,'$.locationList[0].country') as first_preferred_country
        , JSON_VALUE(locationList,'$.locationList[?(@country=='India')].capital as capital_of_india
FROM shop WHERE _Id='1'

Using OPENQUERY in SQL Server

SELECT * FROM OPENQUERY([LS_TO_ELASTICSEARCH_IN_GATEWAY], 'SELECT _id
        , JSON_ARRAY_FIRST(colors) as first_color
        , JSON_ARRAY_LAST(colors) as last_color
        , JSON_ARRAY_NTH(colors,3) as third_color
        , JSON_VALUE(locationList,''$.locationList[0].country'') as first_preferred_country
        , JSON_VALUE(locationList,''$.locationList[?(@country==''India'')].capital as capital_of_india
FROM shop WHERE _Id=''1''')

Using EXEC in SQL Server (handling larger SQL text)

The major drawback of OPENQUERY is its inability to incorporate variables within SQL statements. This often leads to the use of cumbersome dynamic SQL (with numerous ticks and escape characters).

Fortunately, starting with SQL 2005 and onwards, you can utilize the EXEC (your_sql) AT [LS_TO_ELASTICSEARCH_IN_GATEWAY] syntax. 

DECLARE @MyQuery NVARCHAR(MAX) = 'SELECT _id
        , JSON_ARRAY_FIRST(colors) as first_color
        , JSON_ARRAY_LAST(colors) as last_color
        , JSON_ARRAY_NTH(colors,3) as third_color
        , JSON_VALUE(locationList,''$.locationList[0].country'') as first_preferred_country
        , JSON_VALUE(locationList,''$.locationList[?(@country==''India'')].capital as capital_of_india
FROM shop WHERE _Id=''1'''
EXEC (@MyQuery) AT [LS_TO_ELASTICSEARCH_IN_GATEWAY]