Return results of a sql query as JSON in oracle 12c

Question

Background

I need to fetch a few thousands rows from Oracle and convert them to JSON for use in SlickGrid. Currently I am fetching the rows in PHP,

Answer 1

The release 12.2 includes new capabilities for generating JSON documents directly from SQL queries. The easiest way to achieve the goal is to use the functions: JSON_OBJECT and JSON_ARRAYAGG.

create table tab as
    select level col1, 'value '||level col2 from dual connect by level <= 2
/ 

select max (rownum) rn, json_arrayagg (
    json_object (
        key 'col1' value col1,
        key 'col2' value col2
    ) format json returning clob 
) as json_doc
from tab;

Result:

        RN JSON_DOC                                                                        
---------- ---------------------------------------------------------
         2 [{"col1":1,"col2":"value 1"},{"col1":2,"col2":"value 2"}] 

Test with large amount of data:

select rn, length (json_doc) json_size, json_doc from (
    
    cross join (select dummy from dual connect by level <= 1e5) 
    );

        RN  JSON_SIZE JSON_DOC                                                                        
---------- ---------- ---------------------------------------------------------
    200000    5600001 [{"col1":1,"col2":"value 1"},{"col1":2,"col2":"value 2"},

On the slow test machine it took ~1 sec. to create 5,6M JSON.

---

In the release 19c the syntax of the the function JSON_OBJECT is simplified.
The query above will look now like this:

select json_arrayagg (  
    json_object (*) returning clob   
) as json_doc  
from tab;

On Live SQL.