PostgreSQL中JSON列的行數

Question

使用Postgres的IM，我有一個JSON列，這實際上是包含2D結構，例如在此列中的內容是

[ 
    {"in_id":1,"item":"Firsty"}, 
    {"in_id":2,"item":"Second"}, 
    {"in_id":3,"item":"Third"} 
] 

我想添加一個新的排進這個JSON列"Fourth"，以便更新後，這應該是像

[ 
    {"in_id":1,"item":"Firsty"}, 
    {"in_id":2,"item":"Second"}, 
    {"in_id":3,"item":"Third"}, 
    {"in_id":4,"item":"Fourth"} 
] 

想獲得總排在此列，然後加1，然後用文Fourth

更新

有什麼想法？

Answer 1

設置：

create table json_test (id int primary key, val json); 
insert into json_test values 
(1, 
'[ {"in_id":1,"item":"Firsty"}, 
    {"in_id":2,"item":"Second"}, 
    {"in_id":3,"item":"Third"}]'); 

使用json_array_elements()和json_agg()。

with base_query as (
    select json_array_elements(val) elements 
    from json_test 
    where id = 1 
    ), 
union_query as (
    select elements::text 
    from base_query 
    union 
    select '{"in_id":' || count(*)+ 1 || ',"item":"Fourth"}' 
    from base_query 
    ) 
update json_test 
set val = 
    (select json_agg(elements::json) 
    from union_query) 
where id = 1; 

結果：

select * from json_test; 

id |               val              
----+--------------------------------------------------------------------------------------------------------------------- 
1 | [{"in_id":1,"item":"Firsty"}, {"in_id":2,"item":"Second"}, {"in_id":3,"item":"Third"}, {"in_id":4,"item":"Fourth"}] 
(1 row)