我们正在使用Postgres。在一个表中,我们有一个JSON类型的列。
如何找到存储在特定行中的JSON大小?如何找到该列中具有最大JSON数据大小的行?
我们正在使用Postgres。在一个表中,我们有一个JSON类型的列。
如何找到存储在特定行中的JSON大小?如何找到该列中具有最大JSON数据大小的行?
如果你想知道存储一列需要多少字节,那么可以使用
pg_column_size(any) - 用于存储特定值(可能已压缩)所使用的字节数
例子:
SELECT pg_column_size(int2) AS int2, pg_column_size(int4) AS int4,
pg_column_size(int8) AS int8, pg_column_size(text) AS text,
pg_column_size(bpchar) AS bpchar, pg_column_size(char) AS char,
pg_column_size(bool) AS bool, pg_column_size(to_json) AS to_json,
pg_column_size(to_jsonb) AS to_jsonb,
pg_column_size(json_build_object) AS json_build_object,
pg_column_size(jsonb_build_object) AS jsonb_build_object,
octet_length(text) AS o_text, octet_length(bpchar) AS o_bpchar,
octet_length(char) AS o_char, octet_length(to_json::text) AS o_to_json,
octet_length(to_jsonb::text) AS o_to_jsonb,
octet_length(json_build_object::text) AS o_json_build_object,
octet_length(jsonb_build_object::text) AS o_jsonb_build_object
FROM (SELECT 1::int2, 1::int4, 1::int8, 1::text, 1::char, '1'::"char",
1::boolean, to_json(1), to_jsonb(1), json_build_object(1,'test'),
jsonb_build_object(1,'test')
) AS sub
结果:
int2 | int4 | int8 | text | bpchar | char | bool | to_json | to_jsonb | json_build_object | jsonb_build_object | o_text | o_bpchar | o_char | o_to_json | o_to_jsonb | o_json_build_object | o_jsonb_build_object
------+------+------+------+--------+------+------+---------+----------+-------------------+--------------------+--------+----------+--------+-----------+------------+---------------------+----------------------
2 | 4 | 8 | 5 | 5 | 1 | 1 | 5 | 20 | 18 | 21 | 1 | 1 | 1 | 1 | 1 | 14 | 13
获取具有最大json值的行只需要按照 pg_column_size(json_column) desc limit 1
进行排序。
select max(pg_column_size(json)) from table;
select id, pg_column_size(json)
from table
group by id
order by max(pg_column_size(json)) desc limit 1;
对我来说似乎可以工作,但我不是很专家。
字符串中的字节数
t=# with d(j) as (values('{"a":0}'),('{"a":null}'),('{"abc":0}'))
select j,octet_length(j) from d;
j | octet_length
------------+--------------
{"a":0} | 7
{"a":null} | 10
{"abc":0} | 9
(3 rows)
t=# with d(j) as (values('{"a":0}'),('{"a":null}'),('{"abc":0}'))
select j from d order by octet_length(j) desc limit 1;
j
------------
{"a":null}
(1 row)
octet_length
。此外,我建议您如何在Postgres 9.1中查找JSON的大小,因此无论具有有效JSON结构的文本是什么,它仍然是文本 - 而获取此类JSON结构文本字段的大小的最佳方法是我认为是 octet_length
。请为@Łukasz Kamiński的答案点赞 - 他回答得很好。他还展示了JSON和jsonb之间的差异,非常完美。 - Vao Tsun