question

Here's the terraform script to show what I've configured so far.

 # Configure the Azure provider
 terraform {
   required_providers {
     azurerm = {
       source  = "hashicorp/azurerm"
       version = "~> 2.65"
     }
   }
    
   required_version = ">= 0.14.9"
 }
    
 provider "azurerm" {
   features {}
 }
    
 locals {
   tags = {
     Owner  = "Me"
   }
 }
    
 //--------------------------------------
 //  Resource Group
 //
 resource "azurerm_resource_group" "rg" {
   name     = "MyRG"
   location = "australiaeast"
   tags = local.tags
   lifecycle {
     ignore_changes = [
       tags
     ]
   }
 }
    
 //--------------------------------------
 //  IoT Hub
 //
 resource "azurerm_iothub" "iothub" {
   name                = "My-IoTHub"
   resource_group_name = azurerm_resource_group.rg.name
   location            = azurerm_resource_group.rg.location
    
   sku {
     name     = "B1"
     capacity = "1"
   }
    
   tags = local.tags
   lifecycle {
     ignore_changes = [
       tags
     ]
   }
 }
    
 //--------------------------------------
 //  Database Server
 //
 resource "azurerm_mssql_server" "sqlserver" {
   name                         = "my-sql-server"
   resource_group_name          = azurerm_resource_group.rg.name
   location                     = azurerm_resource_group.rg.location
   version                      = "12.0"
   administrator_login          = var.administrator_login
   administrator_login_password = var.administrator_password
   minimum_tls_version          = "1.2"
    
   tags = local.tags
   lifecycle {
     ignore_changes = [
       tags
     ]
   }
 }
    
 resource "azurerm_mssql_firewall_rule" "example" {
   name             = "FirewallRule1"
   server_id        = azurerm_mssql_server.sqlserver.id
   start_ip_address = "0.0.0.0"
   end_ip_address   = "0.0.0.0"
 }
    
 //--------------------------------------
 //  Database
 //
 resource "azurerm_mssql_database" "database" {
   name           = "my-db"
   server_id      = azurerm_mssql_server.sqlserver.id
   collation      = "SQL_Latin1_General_CP1_CI_AS"
   max_size_gb    = 1
   read_scale     = false
   sku_name       = "Basic"
   zone_redundant = false
    
   tags = local.tags
   lifecycle {
     ignore_changes = [
       tags
     ]
   }
 }
    
 //--------------------------------------
 //  Streaming job - Output (to database)
 //
 resource "azurerm_stream_analytics_output_mssql" "output" {
   name                      = "my-job-output"
   stream_analytics_job_name = azurerm_stream_analytics_job.iot-to-db.name
   resource_group_name       = azurerm_stream_analytics_job.iot-to-db.resource_group_name
    
   server   = azurerm_mssql_server.sqlserver.fully_qualified_domain_name
   user     = azurerm_mssql_server.sqlserver.administrator_login
   password = azurerm_mssql_server.sqlserver.administrator_login_password
   database = azurerm_mssql_database.database.name
   table    = "MyTable"
 }
    
 //--------------------------------------
 //  Streaming job - Input (from MQTT)
 //
 resource "azurerm_stream_analytics_stream_input_iothub" "input" {
   name                         = "my-input"
   stream_analytics_job_name    = azurerm_stream_analytics_job.iot-to-db.name
   resource_group_name          = azurerm_stream_analytics_job.iot-to-db.resource_group_name
   endpoint                     = "messages/events"
   eventhub_consumer_group_name = "$Default"
   iothub_namespace             = azurerm_iothub.iothub.name
   shared_access_policy_key     = azurerm_iothub.iothub.shared_access_policy[0].primary_key
   shared_access_policy_name    = "iothubowner"
    
   serialization {
     type     = "Json"
     encoding = "UTF8"
   }
 }
    
 //--------------------------------------
 //  Streaming job
 //
 resource "azurerm_stream_analytics_job" "my-job" {
   name                                     = "my-job"
   resource_group_name                      = azurerm_resource_group.rg.name
   location                                 = azurerm_resource_group.rg.location
   compatibility_level                      = "1.2"
   data_locale                              = "en-AU"
   events_late_arrival_max_delay_in_seconds = 60
   events_out_of_order_max_delay_in_seconds = 50
   events_out_of_order_policy               = "Adjust"
   output_error_policy                      = "Stop"
   streaming_units                          = 1
    
   tags = local.tags
   lifecycle {
     ignore_changes = [
       tags
     ]
   }
    
   transformation_query = <<QUERY
     SELECT *
     INTO [output]
     FROM [input]
 QUERY
    
 }

Hello @Exie-7304,
Thanks for the ask and using the Microsoft Q&A platform .
I am not terrform literate but then I have a hypothesis that may the message coming in are having a different serialization format . At this time its is set to

serialization {
type = "Json"
encoding = "UTF8"
}

This what i tried on my side I have a working ASA with EH with serialization format as JSON , I update the serialization of somethig else . The message stopped showing up on the ASA query .

You can test serialization from the portal UI .

Please do let me know how it goes .
Thanks
Himanshu
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@Exie-7304 did you find the solution, if yes please share here, I am also facing the same issue via terraform