如何获取postgres中的字段计数？

Question

I have a table orders whose structure is like this:

create table orders (id serial primary key, created_at timestamp, updated_at timestamp, product_id varchar[]);

I for the product_id I am inserting data like this:

insert into orders values (1,now(),now(),'{"1","2"}');

the product_id holds the different products that were ordered in a particular order. There is a entry in products table for each of the product_id .

Now I want to get the counts of the product_id for a particular order.

Example: For the above insertion I made, I should get something like:

Id    Count
1     2

How is it possible is postgresql?

Edit: Sorry for messing with the create table query. It's a varchar[] instead of varchar(255)

Answer 1

You can convert the value to an array and measure the number of values:

select o.*, cardinality(product_id)
from orders o

Answer 2

DDL:

CREATE TABLE tbl1 (id integer, count json);

INSERT INTO tbl1 (id, count) values (1, '["1", "2"]'::json), (2, '["3", "45"]');

Query:

 SELECT id, sum(json_array_length(count)) as count from tbl1 group by id order by id;

Result:

 id | count 

----+-------

  1 |     2

  2 |     2

I do hope it helps