Best way to modify a DB Table from a work area in ABAP - abap

Question

I want to find out the best solution for modifying a DB table from work area in a loop.
There are several ways to achieve that, first;
LOOP AT itab INTO wa.
wa-flag = 'X'.
MODIFY zblabla FROM wa.
ENDLOOP.
and field symbol;
LOOP AT ITAB ASSIGNING <WA>.
<WA>-flag = 'X'.
ENDLOOP.
Or, should I modify the DBtable from whole internal table ?
modify zblabla from it.
I'm not sure which one is a better approach for less than 50 entries. (I also want to know which one is better with much more entries. )
Thanks.

Answer 1

Your first example (the one with LOOP AT ITAB ASSIGNING <WA>) does not actually change the database. It only changes the data in memory. However, you can afterwards do UPDATE zblabla FROM TABLE itab. which sends the whole table back to the database at once.
When every single line of the table changed, this is far faster than changing every line individually. But when only a few lines of the table are actually different, this is quite wasteful and it will likely be faster to update only the lines which actually changed using MODIFY.
Another option which can sometimes be used to update database content without even loading it into the application server is the UPDATE database_table SET field = value WHERE condition command.
UPDATE zblabla SET flag = 'X'.
Would set the flag to 'X' for every single row in the table right on the database without even having to SELECT anything.
In your example it would be by far the fastest method, but in the real world you rarely have problems which are so trivial.
UPDATE ... SET ... WHERE ... should also be preferred over MODIFY for single entries when the table you have is very wide and you didn't change most of it because it allows you to specify the fields you want to change. You also must use it when you don't got your data through a SELECT * but instead only queried individual fields.

Answer 2

First modify the data in the loop using a field symbol
LOOP AT ITAB ASSIGNING <WA>.
<WA>-flag = 'X'.
ENDLOOP.
i would suggest you to use UPDATE over MODIFY.
UPDATE DBTAB from TABLE ITAB.
If you want to use Modify statement to update the DB.
MODIFY DBTAB from ITAB.

Answer 3

modify a internal table using transporting and where clauses to specify which fields will be altered using the whole key of the table and then using the internal table change the transparent table (database table).
wa_X-field1 = "something". "where wa_X is of the same type of the table e.g. has the same "fields.
wa_X-field2 = "other something".
MODIFY it_tableX FROM wa_X TRANSPORTING field1 field2 WHERE key1 = wa_X-key1 "(first key)
key2 = wa_X-key2. "(last key)
MODIFY tableX FROM TABLE it_tableX.
This is usually better because it increases performance and assures that you only alter the lines of the table that you mean to change.
Hope this helps.