Home/ Questions/Q 1031295
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-05-16T13:54:18+00:00

I’m interested in whether a SELECT FOR UPDATE query will lock a non-existent row.

  • 0

I’m interested in whether a SELECT FOR UPDATE query will lock a non-existent row.

Example

Table FooBar with two columns, foo and bar, foo has a unique index.

  • Issue query SELECT bar FROM FooBar WHERE foo = ? FOR UPDATE
  • If the first query returns zero rows, issue a query
    INSERT INTO FooBar (foo, bar) values (?, ?)

Now is it possible that the INSERT would cause an index violation or does the SELECT FOR UPDATE prevent that?

Interested in behavior on SQLServer (2005/8), Oracle and MySQL.

Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Editorial Team

    In Oracle, the SELECT … FOR UPDATE has no effect on a non-existent row (the statement simply raises a No Data Found exception). The INSERT statement will prevent a duplicates of unique/primary key values. Any other transactions attempting to insert the same key values will block until the first transaction commits (at which time the blocked transaction will get a duplicate key error) or rolls back (at which time the blocked transaction continues).

    • 0