Use select for update in Cursors and DML

select for update behavior is based on the value of the configuration parameter select for update.

0 – select for update is available only through cursors.
1 – you can use select for update at the language level, outside of a cursor context.

select for update is supported for language statements and for cursors.
Exclusive locks are acquired for qualifying rows of select for update, thereby blocking other readers and writers provided that you are:
- Using datarows-locked tables
- Using the command within a transaction-context, or in chained mode
select for update can have an order by clause for both language statements and cursors. Using an order by clause with a for update clause allows the cursor to be updatable.