UPDATE SQL string substitution from another table

Question

Hi - I've come across a tricky situation where I would want to update a column in all the relevant rows of a table with values obtained from another table WITHIN the same column update using string concatenation. im not getting any clean way of doing this.
The goal is to achieve something like this:
UPDATE table1 set col1 =
'LANG_ID=(%s),'||
'_CHALLENGE_RESPONSE_=(%s),'||
'CRDN_NAM=(%s),'||
'CLNT_MODE=(%s),'||
'PTY_ID=(%s),'||
'CRDN_VAL=(%s),' ||
'USER_TZ_COD=(%s),' ||
'GTS_USER_ID=(%s),'||
'SP_ID=(%s),' ||
'SP_ALIAS=(%s),' ||
'ORIG_CLNT_ID=(%s)'
where table1.col1 is null
and to substitute the (%s) with data from another table2*. An example is:
update table1 set col1=
'LANG_ID=(select LANG_ID from table2* where USER_ID = (select USER_ID from table1))' ||
'_CHALLENGE_RESPONSE_=((select CHALLENGERESPONSE_ from table2* where USER_id = (select USER_ID from table1)),' ||
etc for the rest of the values

Answer 1

I tried this -although the database shows that the affected rows are updated! but querying the table doesn't show the values in the column!
select col1 from table1 where col1 is null
shows back the original content (DESPITE it showing me xxx rows updated!)
UPDATE table1 t1
SET col1 = (SELECT 'LANG_ID=('||lang_id||')_CHALLENGE_RESPONSE_=('||
CHALLENGERESPONSE_|| ...*
FROM table2 t2
WHERE t1.user_id = t2.user_id)
WHERE t1.col1 is null;