Fix #31 - Created rule G-4250: Avoid using identical conditions in different branches of the same IF or CASE statement.

Author: kibeha

docs/4-language-usage/4-control-structures/2-case-if-decode-nvl-nvl2-coalesce/g-4250.md

@@ -0,0 +1,46 @@
+# G-4250: Avoid using identical conditions in different branches of the same IF or CASE statement.
+
+!!! warning "Major"
+    Maintainability, Reliability, Testability
+
+## Reason
+
+Conditions are evaluated top to bottom in branches of a `case` statement or chain of `if`/`elsif` statements. The first condition to evaluate as true leads to that branch being executed, the rest will never execute. Having an identical duplicated condition in another branch will never be reached and will be dead code.
+
+## Example (bad)
+
+``` sql
+declare
+   l_color types_up.color_code_type;
+begin
+   case l_color
+      when constants_up.co_red   then 
+         my_package.do_red();
+      when constants_up.co_blue  then 
+         my_package.do_blue();
+      when constants_up.co_red then  -- never reached
+         my_package.do_black();      -- dead code
+      else null;
+   end case;
+end;
+/
+```
+
+## Example (good)
+
+``` sql
+declare
+   l_color types_up.color_code_type;
+begin
+   case l_color
+      when constants_up.co_red   then 
+         my_package.do_red();
+      when constants_up.co_blue  then 
+         my_package.do_blue();
+      when constants_up.co_black then 
+         my_package.do_black();
+      else null;
+   end case;
+end;
+/
+```