CASE is an
expression that lets you do some IF/THEN/ELSE logic to produce a value.
COALESCE is a function that returns the first non-NULL value passed into it. If
all parameters passed in are NULL, it returns NULL. The type returned by
COALESCE is the type of the first non-NULL parameter.
ISNULL is a
function that works like COALESCE. But it only takes two parameters. It is a Microsoft
specific function. The return type is the type of the first parameter passed
in. A related function is NULLIF, which will return NULL if the two parameters
passed in are the same. Otherwise it returns the first parameter.
The IIF
function is an unusual one. It is like the ternary operator in the C
programming language. It accepts a BOOLEAN expression as the first parameter.
If that evaluates to TRUE, then the second parameter is returned. Otherwise the
third parameter is returned.
The CHOOSE function is another oddity. You pass
it an index plus a list of values. It will return the value in the list at the
location specified by the index. Not sure how valuable such a function is.
