help

I read your document about the porting from Oracle to PgSql and I would 
like to know if
you can say to me if there is an equivalent on an the option NOWAIT for 
a request
SELECT ... FOR UPDATE (for Oracle) under PgSql.

This option don't wait a previus unlock and return the information like 
the line can't be lock.

Oracle:
SELECT * FROM toto WHERE id =4 and value = 'hello' FOR UPDATE NOWAIT;

PsSql:
????????????????????????


Tanks a lot....