Now I'm confused. What is the link between EVAL(), CURVAL(), and OLDVAL()

On a totally unrelated topic, I had to write goofy SQL code for a view with a concatanated foreign key that I couldn't believe worked. The WHERE clause was like:

WHERE x = LEFT(?table.field,5) AND y = RIGHT(?table.field,4)

Strange, huh? In the past, I've seen problems with WHERE clauses using two parameterized statements in the same query.

>>There is great confusion in the land between the uses of (), &, and EVAL().
>
>The only time I routinely use EVAL(), for what it's worth, is as a partner to CURVAL() and OLDVAL(). Makes a handy mnemonic device...