sql - Update Query with select and row lock -

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update mytable set node_index=0 id in (         select              id          mytable                       rownum<=10 , procs_dt null            order cret_dt,prty desc)

i got query part of previous answer question. how lock rows in select query make sure no other thread on writes update.

it's not clear me have problem seem think have.

updating row in table inherently places row-level lock on row. no other session can update row until release lock ending transaction committing or rolling back. once complete transaction, other sessions free overwrite update. there no need or benefit locking rows in select.

if trying write application avoid lost updates (i.e. want avoid session updating same rows did after committed transaction without showing other user updated data first), application need implement sort of additional locking. efficient implement optimistic locking using sort of last_update_timestamp column in table. assuming added column table if doesn't have one, select last_update_timestamp whenever queried data present user , specify last_update_timestamp in update. if update updated 1 row, know no 1 had changed data since queried it. if update updated 0 rows, know data had changed since had queried , application need take appropriate action (i.e. re-querying data, re-presenting user, asking user whether keep of uncommitted changes had made, etc.).

your query have problem, however. select statement not doing think (or intend) do. query gets arbitrary 10 rows mytable procs_dt null , orders arbitrary 10 rows. 

         select              id          mytable                       rownum<=10 , procs_dt null            order cret_dt,prty desc

assuming want "top 10" results, need order by in subquery before applying rownum predicate, i.e.

         select              id          (select *                  mytable                 procs_dt null                 order cret_dt, prty desc)                       rownum<=10

or use analytic function, i.e.

         select              id          (select m.*,                       rank() on (order cret_dt, prty desc) rnk                  mytable m                 procs_dt null)                       rnk<=10

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