检查对象键在给定jsonb阵列看起来像这样的对象

Question

的JSON数组中出现两次：

[ 
    { "type": "foo", "desc": "example" }, 

    { "type": "foo", "desc": "second example" }, 

    { "type": "bar", "desc": "third example" } 
] 

我想创建如果{ "type": "foo" }出现两次返回true的PostgreSQL的功能。

Answer 1

使用jsonb_array_elements()，例如：

with data(js) as (
    select 
     '[ 
     { "type": "foo", "desc": "example" }, 
     { "type": "foo", "desc": "second example" }, 
     { "type": "bar", "desc": "third example" } 
     ]'::jsonb 
) 
select elem->>'type' as "type", count(elem->'type') 
from data, jsonb_array_elements(js) elem 
group by 1; 

type | count 
------+------- 
foo |  2 
bar |  1 
(2 rows)  

的功能应该是这样的：

create or replace function check_duplicates(source jsonb, key text) 
returns boolean language sql as $$ 
    select max(count) > 1 
    from (
     select count(elem->key) 
     from jsonb_array_elements(source) elem 
     group by elem->key 
     ) s 
$$; 

用法：

with data(js) as (
    select 
     '[ 
     { "type": "foo", "desc": "example" }, 
     { "type": "foo", "desc": "second example" }, 
     { "type": "bar", "desc": "third example" } 
     ]'::jsonb 
) 
select check_duplicates(js, 'type') 
from data; 

check_duplicates 
------------------ 
t 
(1 row) 

Answer 2

这里，做一个函数。

CREATE OR REPLACE FUNCTION more_than_two_foos(s jsonb) RETURNS bool AS $$ 
DECLARE 
    c integer; 
BEGIN 
    SELECT count(*) 
    FROM (
     SELECT 1 
     FROM jsonb_array_elements(s) 
     WHERE value->>'type'='foo' 
     LIMIT 2 
    ) t 
    INTO c; 
    RETURN c>=2; 
END; 
$$ LANGUAGE plpgsql IMMUTABLE STRICT; 

下面是一个例子：

$ SELECT more_than_two_foos('[ 
    { "type": "foo", "desc": "example" }, 
    { "type": "foo", "desc": "second example" }, 
    { "type": "bar", "desc": "third example" } 
]'); 
more_than_two_foos 
-------------------- 
t 
(1 row) 

$ SELECT more_than_two_foos('[ 
    { "type": "foo", "desc": "second example" }, 
    { "type": "bar", "desc": "third example" } 
]'); 
more_than_two_foos 
-------------------- 
f 
(1 row) 

的想法是，它通过使用jsonb_array_elements的jsonb数组的元素，并计算有type等于foo的元素。