sql - Case statement with aggregate and like clause

i'm struggling case statement in mssql 2012. i've looked around other answers, although i've got help, none seem fix problem.

case firstname     when len(ltrim(rtrim(firstname))) > 11 'blah'     else 'blahblah' end test

i getting syntax error, on '>' character.

originally,

case firstname     when ltrim(rtrim(firstname)) '% %' 'blah'     else 'blahblah' end test

but thought there may have been sensitivity on keyword, changed '>', same thing.

probably dumb question, i've been banging head couple of hours , insight appreciated.

try version:

(case when len(ltrim(rtrim(firstname))) > 11 'blah'       else 'blahblah'  end) test

the case statement has 2 versions. 1 variable used constant expressions:

(case firstname       when 'arnold' . . .       when 'betty' . . .  end)

the second version (which 1 use) takes conditional each part:

(case when firstname = 'arnold' . . .

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