求SQL语句的写法

想下面的代码(VB.NET),在SQL中应该怎么写呀

VB.NET code:

If Str_delx = "a" Then

ElseIf Str_delx = "b" Then

ElseIf Str_delx = "c" Then

Else

End If

---

SQL code:
CASE Str_delx WHEN 'A' THEN .. WHEN 'B' THEN .. WHEN 'C' THEN .. ELSE ..END

---

SQL code:
case
when Str_delx = 'a' Then xxx1
when Str_delx = 'b' Then xxx2
when Str_delx = 'c' Then xxx3
Else xxx4
End

---

case when Str_delx = "a" then ...
when Str_delx = "b" then ...
when Str_delx = "c" then ...
end

---

SQL code:
case when

---

SQL code:
If @Str_delx = 'a'
begin
end
Else If @Str_delx = 'b' Then
begin
end
Else I