How to generate JSON in Oracle for a CLOB that is > 32k (e.g. 60,000 characters)?

Question

1 ) I have to make json from oracle select query which has three approach i can follow .

SELECT JSON_ARRAY(json_object('id'         VALUE employee_id, 
                   'data_clob'    VALUE data_clob
                     )) from tablename;

also i have tried with this approach

2) If you are unable to patch/work with that version there is an excellent package written by Lewis Cunningham and Jonas Krogsboell: PL/JSON * http://pljson.sourceforge.net/

It's an excellent package (I have used it in numerous database installations).

The examples included are good and cover most scenarios.

declare 
  ret json;
begin
  ret := json_dyn.executeObject('select * from tab');
  ret.print;
end;
/

Mention In this answer too but not work for such big clob. Return results of a sql query as JSON in oracle 12c

3) The other approach can be we can concatenate the string after the select query.

FOR rec IN (SELECT employee_id, data_clob
                FROM tablename) LOOP
      IF i <> 1 THEN
        v_result := v_result || ',';
      END IF;

      v_result := v_result || '{"employee_id":' || to_char(rec.employee_id) || ',"data_clob": ' || rec.data_clob || '}';

      i := i + 1;
    END LOOP;
    v_result := v_result || ']}'; 

3 approach solve my problem but i don't want to run for loop . Is there is any solution in oracle to handle this .

I check for solution but that don't work without for loop.

https://technology.amis.nl/2015/03/13/using-an-aggregation-function-to-query-a-json-string-straight-from-sql/

url has provide some solution , i tried this but not working .Same issue is coming.

ORA-22835: Buffer too small for CLOB to CHAR or BLOB to RAW conversion (actual: 57416, maximum: 4000)

Could you able to tell me how it can be done ?

Answer 1

Since 12.2 version you can do:

select 
  json_object(
     'body' value v_clob 
     returning clob
  )
from dual;

Original answer:

In answer to this question:

3 approach solve my problem but i don't want to run for loop . Is there is any solution in oracle to handle this .

Strings can be concatenated without looping by using Oracle's LISTAGG function:

SELECT '{"employees":[' || LISTAGG('{"employee_id":' || to_char(employee_id)
                      || ',"data_clob":"' || data_clob || '"}', ',')
              WITHIN GROUP (ORDER BY employee_id) || ']}' AS json
FROM tablename;

However, as you've pointed out in the comments, LISTAGG has a limit of 4000 characters. The following is more complex/fiddly but should cope beyond this limit:

SELECT '{"employees":[' || dbms_xmlgen.convert(
         RTRIM(XMLAGG(XMLELEMENT(E,'{"employee_id":' || to_char(employee_id)
                                 || ',"data_clob":"' || data_clob || '"}',',')
                      .EXTRACT('//text()') ORDER BY employee_id).GetClobVal(),',')
       , 1) || ']}' AS json
FROM tablename;

XMLAGG handles CLOBs but the EXTRACT function has the side-effect of escaping certain characters (e.g. from " to "). The query above converts these back (e.g. from " to ") using the dbms_xmlgen.convert function - see this answer for further details.

SQL Fiddle demo: http://sqlfiddle.com/#!4/5b295/40

Answer 2

By default the new json_* functions return a varchar2(4000). You can change this in the returning clause.

If you have extended data types enabled, you can change this to a varchar2(32767). But only the *agg functions support clob.

from here

SELECT length(JSON_ARRAYAGG( 
         JSON_OBJECT( 
           KEY 'object_type' VALUE object_type, 
           KEY 'object_name' VALUE object_name 
         ) 
       returning clob) 
       ) array_size
FROM   all_objects;

ARRAY_SIZE  
5772072  

18c also has full support for clobs in the JSON* functions

Answer 3

In 12.2 json_* functions handle clobs fine. Use clause Returning clob

create table t( c clob, constraint t_chk check (c is json));
declare
    v_clob clob;
begin
    for i in 1..10000 loop
        v_clob := v_clob || 'asdasdadasdasdasdasdasdasdasd';
    end loop;

    insert into t(c) 
    select 
        json_object
        (
           'body' value v_clob returning clob
         )
    from
        dual;
end;