== Why is this an issue?

A ``++CASE++`` and a chain of ``++IF++``/``++ELSE IF++`` statements is evaluated from top to bottom. At most, only one branch will be executed: the first one with a condition that evaluates to ``++true++``.


Therefore, duplicating a condition automatically leads to dead code. Usually, this is due to a copy/paste error. At best, it's simply dead code and at worst, it's a bug that is likely to induce further bugs as the code is maintained, and obviously it could lead to unexpected behavior. 

=== Noncompliant code example

[source,sql]
----
IF @x = 1
  PRINT 'A'
ELSE IF @x = 2
  PRINT 'B'
ELSE IF @x = 1 -- Noncompliant
  PRINT 'C'

SELECT
  CASE col1
    WHEN 1 
      THEN 'A'
    WHEN 2 
      THEN 'B'
    WHEN 1  -- Noncompliant
      THEN 'C'
    ELSE 'D'
  END
FROM table1
----

=== Compliant solution

[source,sql]
----
IF @x = 1
  PRINT 'A'
ELSE IF @x = 2
  PRINT 'B'
ELSE IF @x = 3
  PRINT 'C'

SELECT
  CASE col1
    WHEN 1 
      THEN 'A'
    WHEN 2 
      THEN 'B'
    WHEN 3 
      THEN 'C'
    ELSE 'D'
  END
FROM table1
----


ifdef::env-github,rspecator-view[]

'''
== Implementation Specification
(visible only on this page)

=== Message

This condition duplicates the one on line n.


include::../highlighting.adoc[]

'''
== Comments And Links
(visible only on this page)

include::../comments-and-links.adoc[]

endif::env-github,rspecator-view[]
