async function commentFor(knex, target) {
            const columnSpecifier = target.columnName
              ? `N'Column', :columnName`
              : 'NULL, NULL';
            const result = await knex
              .from(
                knex.raw(
                  `fn_listextendedproperty(N'MS_Description', N'Schema', :schemaName, N'Table', :tableName, ${columnSpecifier})`,
                  target
                )
              )
              .select('value AS comment')
              .first();
            return result ? result.comment : undefined;
          }
Returns the comment for `target`, if any.

@param {Knex} knex
@param {{schemaName: string, tableName: string, columnName?: string}} target
@returns {Promise<string|undefined>}