This note is in Hasura.Backends.MSSQL.DDL.EventTrigger. It is referenced at:
We do not have JSON datatype in SQL Server. But since in ‘mkAllTriggersQ’ we ensure that all the values in the payload column of hdb_catalog.event_log is always a JSON. We can directly decode the payload value and not worry that the decoding will fail.
We ensure that the values in ‘hd_catalog.event_log’ is always a JSON is by using the ‘FOR JSON PATH’ MSSQL operand when inserting value into the ‘hdb_catalog.event_log’ table.