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
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
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
