Re: Converting sql anywhere to postgres

On 8/15/23 08:04, Russell Rose | Passfield Data Systems wrote:
> Hi there
> 
> I am trying to convert a SQL Anywhere database to postgres. Within SQL 
> anywhere a field can have a default value of ‘last user’. This means 
> that when you perform an update on a table, if the field is not 
> explicitly set then the current user is used. So for instance if I have 
> a field called mod_user in a table, but when I do an update on the table 
> and do not set mod_user then SQL Anywhere sets the field to current_uer. 
> I have tried to replicate this using a postgres trigger in the before 
> update. However, if I do not set the value then it automatically picks 
> up the value that was already in the field. Is there a way to tell the 
> difference between me setting the value to the same as the previous 
> value and postgres automatically picking it up.

Not that I know of. In Postgres an UPDATE is essentially a DELETE of the 
OLD tuple and an INSERT of a new tuple. You cannot determine whether the 
same value in a given field for the OLD/NEW records was explicitly set 
the same or just carried over.

> 
> If the field myfield contains the word ‘me’. Can I tell the difference 
> between:
> 
> Update table1 set field1=’something’,myfield=’me’
> 
> And
> 
> Update table1 set field1=’something’
> 

-- 
Adrian Klaver
adrian.klaver@aklaver.com