pgsql中polygon用法

```sql
SELECT
pl.id,
(select district from (
SELECT
(SELECT string_agg(label,', ') from (SELECT unnest(points_arr) "label")L) as polygon,
block.district as district
FROM
block
)b where b.polygon::POLYGON @> CAST ( '(' || pl.longitude::VARCHAR || ',' || pl.latitude::VARCHAR || ')' AS polygon ) limit 1) as district_name
FROM
parking_lot pl