[大数据]postgresql-json查询

2、例子
json如下，我们需要拿到所有的重量

{"key1":{"key2":[{"weight":10},{"weight":15}]}}

将json存在字段snapshot中
snapshot::json->>'key1‘,是将snapshot文本看作json取出key1值
json_array_elements是查询一个json数组

--weight   
SELECT  json_array_elements(t2.key2Value::json)->'weight' weight from (
--key2Value  ：：：[{"weight":10},{"weight":15}]
SELECT   t1.key1Value ::json->>'key2' key2Value  from (
--key1Value ：：：{"key2":[{"weight":10},{"weight":15}]}
SELECT  snapshot::json->>'key1' key1Value from task_done_info  where  id ='74960048' limit 1
)t1
)t2