In SQL Server 2016 they are added support for outputting your query results in JSON. When you serialize your data to JSON using the FOR JSON clause, a data type conversion happens. The data types are converted from SQL Server data types to JSON supported data types.
For more information on how to convert your result set to JSON: www.sqlserver.info/syntax/json-in-sql-server/
Here is a quick reference table showing the data type conversions that are happening:
| SQL Data Type | JSON Data Type |
|---|---|
| VARCHAR/NVARCHAR | String |
| CHAR/NCHAR | String |
| INT | Number |
| BIGINT | Number |
| FLOAT | Number |
| DECIMAL | Number |
| NUMERIC | Number |
| BIT | Boolean |
| DATETIME | String |
| DATETIME2 | String |
| DATE | String |
| TIME | String |
| DATETIMEOFFSET | String |
| VARBINARY | Base64-encoded string |
| BINARY | Base64-encoded string |
| IMAGE | Base64-encoded string |
| TIMESTAMP | Base64-encoded string |
| ROWVERSION | Base64-encoded string |
| UNIQUEIIDENTIFIER | String |
| MONEY | String |