有条件地包括在presto查询的字段中

Question

我有一个按预期工作的presto查询：

SELECT json_format(cast(MAP(ARRAY['random_name'],
           ARRAY[
             MAP(
                ARRAY['a', 'b', 'c'],
                ARRAY[a, b, c]
            )]
) as JSON)) as metadata from a_table_with_a_b_c;  // a,b,c are all ints

现在我只想在大于0时包含a，b，c，如何更改查询？我可以添加＆＃39; CASE WHEN＆＃39;但似乎我会有＆＃39; a：null＆＃39;而不是没有它。

Answer 1

你可以试试这个：

with rows as ( select row_number() over() as row_id, ARRAY['a', 'b', 'c'] as keys, ARRAY[a, b, c] as vals from a_table_with_a_b_c ) select json_format(cast(MAP(ARRAY['random_name'], ARRAY[ MAP( array_agg(key), array_agg(value) )] ) as JSON)) as metadata from rows cross join unnest (keys, vals) as t (key, value) where value is not null and value > 0 group by row_id;