FOR UPDATE in PLSQL

The FOR UPDATE clause locks the rows selected by the query. Once you have selected a row for update, other users cannot lock or update it until you end your transaction. The FOR UPDATE clause signals that you intend to insert, update, or delete the rows returned by the query, but does not require that you perform one of these operations. A SELECT statement with a FOR UPDATE clause is often followed by one or more UPDATE statements with WHERE clauses.

The FOR UPDATE clause cannot be used with the following other constructs:

·         DISTINCT operator

·         GROUP BY clause

·         set operators

·         group functions