Rewrite post-title with content of custom field?

Hi,

is there any plugin which can rewrite the title of any post with the content of a custom field attached to this post?

If not, can someone please help me with a simple sql-query here? I know how to replace a text, but when it comes to checking a custom field and only do something if there is content, that’s where my wp/sql knowledge stops…

greets
alex