Oracle Update data in Clob datatype column

Question

I am very new to Oracle and Clob datatype.

We have a table with name ABC which has a column of CLOB data type.

The Clob Column "MyClob" has following text data:

{ "UD_1":"John", "UD_2":"Doe", "UD_3":"1011=John Doe"}

When I query the table 'ABC' using below query,

Select Id, 
   JSON_VALUE(MyClob, '$.UD_1') FirstName
   JSON_VALUE(MyClob, '$.UD_2') LastName
   JSON_VALUE(MyClob, '$.UD_3') Status
From Abc

I get the following table:

Id    FirstName  LastName    Status
1     John       Doe         1011=John Doe
2     Jack       Ham         2022=Jack Ham

I want to update only the 'UD_3' value for one of the rows. I am not sure how to write an update query to update the text in Clob column.

Answer 1

You can perform updates to JSON using JSON_MERGEPATCH . To use JSON_MERGEPATCH , in the second argument you will need to pass a JSON object of the key/value pairs that you want to update. See example below.

Another item to note is that the returned value of JSON_MERGEPATCH will remove any unnecessary spaces from the JSON.

SQL> CREATE TABLE sampletable
  2  (
  3      id,
  4      myclob
  5  )
  6  AS
  7      SELECT 1,
  8                EMPTY_CLOB ()
  9             || '{ "UD_1":"John", "UD_2":"Doe", "UD_3":"1011=John Doe"}'
 10        FROM DUAL
 11      UNION ALL
 12      SELECT 2,
 13                EMPTY_CLOB ()
 14             || '{ "UD_1":"Jack", "UD_2":"Ham", "UD_3":"2022=Jack Ham"}'
 15*       FROM DUAL;

Table SAMPLETABLE created.

SQL> SELECT *
  2    FROM sampletable  t
  3         CROSS JOIN
  4         JSON_TABLE (
  5             t.myclob,
  6             '$'
  7             COLUMNS (firstname VARCHAR2 PATH '$.UD_1',
  8                      lastname VARCHAR2 PATH '$.UD_2',
  9*                     status VARCHAR2 PATH '$.UD_3'));

   ID MYCLOB                                                    FIRSTNAME    LASTNAME    STATUS
_____ _________________________________________________________ ____________ ___________ ________________
    1 { "UD_1":"John", "UD_2":"Doe", "UD_3":"1011=John Doe"}    John         Doe         1011=John Doe
    2 { "UD_1":"Jack", "UD_2":"Ham", "UD_3":"2022=Jack Ham"}    Jack         Ham         2022=Jack Ham

SQL> UPDATE sampletable
  2     SET myclob = json_mergepatch (myclob, '{"UD_3":"3033-Devp"}')
  3*  WHERE id = 1;

1 row updated.

SQL> commit;

Commit complete.

SQL> SELECT *
  2    FROM sampletable  t
  3         CROSS JOIN
  4         JSON_TABLE (
  5             t.myclob,
  6             '$'
  7             COLUMNS (firstname VARCHAR2 PATH '$.UD_1',
  8                      lastname VARCHAR2 PATH '$.UD_2',
  9*                     status VARCHAR2 PATH '$.UD_3'));

   ID MYCLOB                                                    FIRSTNAME    LASTNAME    STATUS
_____ _________________________________________________________ ____________ ___________ ________________
    1 {"UD_1":"John","UD_2":"Doe","UD_3":"3033-Devp"}           John         Doe         3033-Devp
    2 { "UD_1":"Jack", "UD_2":"Ham", "UD_3":"2022=Jack Ham"}    Jack         Ham         2022=Jack Ham