How to update a table with huge data

Question

Hi,
I have a scenario where I need to update tables that are having huge data (each table is having more than 10,00000)
I am writing this update in PLSQL block.
Is there any way to improve the performance of this update statement? Please suggest...
Thanks.

Answer 1

user10403630 wrote:
I am storing all tables and columns that needs to be updated in tab_list and forming a dynamic qry.
for i in (select * from tab_list)
loop
v_qry := 'update '||i.table_name||' set '|| i.column_name ' = '''||new_value||'''' ||' where '||i.column_name = ''||old_value||'''';
execute immediate v_qry;
end loop;Sorry to say so but this code is aweful!
Well the only thing to make this even more slow would be to add a commit inside the loop.
Some advices. But I'm not sure which one works in your case.
The fastest way to update a million rows is: write a single update statement. On typical systems this should only run for like a couple of minutes.
if you need to update several tables then write a single update for each table.
If you have different values that need to be updated then find a way how to consider those different values in a single update or merge statement. Either by joining another table or by using some in-lists.
e.g.
update myTable
set mycolumn = decode(mycolumn
                                 ,'oldValue1','newvalue1'
                                 ,'oldValue2','newvalue2'
                                 ,'oldValue3','newvalue3')
where mycolumn in ('oldValue1','oldvalue2','oldvalue3'....);If you need to do this in pl/sql then
1) use bind variables to avoid hard parsing the same statement again and again
2) use bulk binding to avoid pl/sql context switches