PostgreSQL对数组元素聚合基本方法示例

id      author
 2    [张三, 李四, 王五]
 2    [张三, 李四]
 3    [张三]

select item, count(item) as cnt
from (select unnest(journal.author) as item from journal) as tmp
group by item

select item, count(distinct id) as cnt
from journal, unnest(journal.author) as item
group by item

select item, count(item) as cnt
from journal, unnest(journal.author) as item 
group by item