+2  A: 

I think that it's the str_replace function that you want.

As far as I can tell it's not an exact equivalent, as the third parameter is not optional, but the general usage is the same.

Guffa
A: 

How about using the Sybase Replace function?

http://manuals.sybase.com/onlinebooks/group-iq/iqg1250e/iqref/@Generic__BookTextView/37946;pt=37863

Syntax:

REPLACE ( original-string, search-string, replace-string )

Example: SELECT REPLACE( 'abc.def.abc.ghi', 'abc', 'xx' ) FROM iq_dummy

Steve