Connection to SQL Server database using sql_exporter and Prometheus but can't execute custom metrics on db

Question

So, I've went through many of the options to get this set up and none worked with my SQL Server setup except using sql_exporter. There is a successful connection where I can read all the built-in metrics but when I tried my own query on a specific database and its table there is always something wrong with my query such as "Invalid Object" when trying to reach the database. There have been many resources I have attempted to use but would mostly like a custom metric like: https://sysdig.com/blog/monitor-sql-server-prometheus/.

sql_exporter.yml:

# The target to monitor and the collectors to execute on it.
target:
  # Data source name always has a URI schema that matches the driver name. In some cases (e.g. MySQL)
  # the schema gets dropped or replaced to match the driver expected DSN format.
  data_source_name: 'sqlserver://username:password@localhost:1433'

  # Collectors (referenced by name) to execute on the target.
  collectors: [mssql_standard]

# Collector files specifies a list of globs. One collector definition is read from each matching file.
collector_files: 
  - "*.collector.yml"

prometheus.yml:

scrape_configs:
  # The job name is added as a label `job=<job_name>` to any timeseries scraped from this config.
  - job_name: "prometheus"

    # metrics_path defaults to '/metrics'
    # scheme defaults to 'http'.

    static_configs:
      - targets: ["localhost:9090"]

  - job_name: 'sql_server'

    # Override the global default and scrape targets from this job every 5 seconds.
    scrape_interval: 5s

    static_configs:
      - targets: ['localhost:9966']

When I tried the custom metric in the post I linked, sql_exporter crashes instantly no errors. My database is being found in the standard metrics of https://github.com/free/sql_exporter but I am unsure the syntax to execute a simple SELECT db_value FROM db_table. I understand there are ways out there and I've tried so will need assistance. Thank you in advance!