<para>

Update contact names in an accounts table to match the currently assigned

salesmen:

salespeople:

<programlisting>

UPDATE accounts SET (contact_first_name, contact_last_name) =

(SELECT first_name, last_name FROMsalesmen

WHEREsalesmen.id = accounts.sales_id);

(SELECT first_name, last_name FROMemployees

WHEREemployees.id = accounts.sales_person);

</programlisting>

A similar result could be accomplished with a join:

<programlisting>

UPDATE accounts SET contact_first_name = first_name,

contact_last_name = last_name

FROMsalesmen WHEREsalesmen.id = accounts.sales_id;

FROMemployees WHEREemployees.id = accounts.sales_person;

</programlisting>

However, the second query may give unexpected results

if <structname>salesmen</structname>.<structfield>id</structfield> is not a unique key, whereas

if <structname>employees</structname>.<structfield>id</structfield> is not a unique key, whereas

the first query is guaranteed to raise an error if there are multiple

<structfield>id</structfield> matches. Also, if there is no match for a particular

<structname>accounts</structname>.<structfield>sales_id</structfield> entry, the first query

<structname>accounts</structname>.<structfield>sales_person</structfield> entry, the first query

will set the corresponding name fields to NULL, whereas the second query

will not update that row at all.

</para>