Support persist_docs for column descriptions

dbt 0.17.0 adds support for persist_docs = {'columns': true} on all core adapters.

In Apache Spark, column-level comments are only supported during table creation with a full column specification. I think that adding column comments as an alter table command may only be possible for Delta tables.

[cristianoperez]

I changed the syntax from ALTER COLUMN to CHANGE COLUMN and it’s now working. I ran that against 100+ models, around 10 times and no exception

{% macro set_column_description(relation, column_dict) %}  
  {% for column_name in column_dict %}    
    {% set comment = column_dict[column_name]['description'] %}    
    {% set comment_query %}        
      ALTER TABLE {{ relation }} CHANGE COLUMN {{ adapter.quote(column_name) if column_dict[column_name]['quote'] else column_name }} COMMENT '{{ comment }}';      
    {% endset %}      
    {% do run_query(comment_query) %}    
  {% endfor %}
{% endmacro %}

[cristianoperez]

I changed the syntax from ALTER COLUMN to CHANGE COLUMN and it’s now working.

Genius! From the docs, it sure sounds like these are meant to be interchangeable…

Would you be up to open a PR to add spark__alter_column_comment by way of alter table change column?

I will