add sqlserver__alter_column_type macro

[dlarsen5]

resolves dbt-synapse issue 152 incremental table alter column type syntax error

[dataders]

thanks @dlarsen5!

[panasenco]

This macro is not working for me, I'm getting the error [42S22] [Microsoft][ODBC Driver 17 for SQL Server][SQL Server]Invalid column name 'message__dbt_alter'. (207) (SQLExecDirectW).

SQL Server doesn't seem to support doing multiple updates/alters in a single statement without hacking it with something like EXEC().

FWIW this is not actually a big deal for me because I defined my own custom macro that works just fine. I'm not really sure why the dbt team needed to create a new column, copy data, delete the original column, then rename the new column in their original macro.

{% macro sqlserver__alter_column_type(relation, column_name, new_column_type) %}
  {% call statement('alter_column_type') -%}
    alter {{ relation.type }} {{ relation }} alter column {{ column_name }} {{ new_column_type }};
  {%- endcall -%}
{% endmacro %}