Error:
SP2-0027: Input is too long (> 4999 characters)
Cause:
The SQL builder tool used does not support characters over 4999 in a single line command.
So even though the where clause contains 999 value limit within the range of sqlplus but number of characters per line exceeded the 4999 characters.
update xms_ldm_rpt_tab
set valid_for=null
where ldm_key in (1,2,3,..............................999);
Solution:
1) Break the line for entered values in where clause to appear on next line to avoid reaching per line limit of 4999 .
update xms_ldm_rpt_tab
set valid_for=null
where ldm_key in (1,2,3,
.....,
.....,
.....,
.....,
....999);
2) User subquery to pass high range of values to where clause.
update xms_ldm_rpt_tab
set valid_for=null
where ldm_key in (select num from x_table);
Solved !