In DB2 we need to update the field size from 18 to 26? How can we do the same? What will happen (in subprograms) while doing the same? Where we need to increase the field size (In copybook or...)? Please give me brief description?
By updating field size, do you mean increasing the length of a column size from 18 to 26 chars?
Assuming the above, in this case, the DBA will increase the column length using ALTER TABLE command. Generally, we do not have such privileges.
Once we have the modified column length in the table, we can re-generate the DCLGEN to have modified host variable declarations. The same will be used in the program & sub-programs. If we have used any working storage variables for any of the modified columns for some processing, then those variables have to be modified to reflect the column length changes.