What key is this song in?

[arren31]

https://sheetmusiccover.altervista.org/download.php?file=./pdf/9/23.pdf
 I guessed that it was in the key of B, but when I searched up what the key signature for B looks like, it was different (it had sharps instead of flats, and the accidentals were in different places). My second guess was it was in the key of F#, but when I searched up what the key signature for F# looks like, it was different. So, I don't know what key it is :3
Also, I'm learning the violin. That's why it says violin on the sheet music, and also, that's why there's no bass clef on the sheet music.

[arren31]

Nvm, figured it out now, it's in Db

[dcstudio]

   good because when you said the key of B had sharps instead of flats I got a bit worried. 5 sharps is B--5 flats is Db.  learn your key signatures my friend... it's a good thing to know.

[jimroof]

Easy way to tell the keys from the key signature.

If it is flats, it works this way...

No flats... C or the relative minor, Am (conveniently, a minor third lower than C)
1 flat... F or the relative minor Dm (ditto for all relative minors)
If it is 2 - 7 flats, the key is the next to last FLAT in the signature OR the relative minor.  Example - you see 3 flats, Bb, Eb and Ab.  The key?  Eb, the next to last flat (going left to right) OR the relative minor (Cm - a minor third lower than the Eb).

Sharps are even easier.  Look at the last sharp.  That will be the leading tone 7th in the MAJOR scale.  Example, you have just one sharp - F# - you are in the key of G or the relative minor Em.  You have 4 sharps, F#, C#, G# and D#.  You are in the key of E.  The last sharp is D#, the seventh note of the major scale (leading tone of the tonic) OR you are in the relative minor key of C#m.

So, how to tell if you are actually the major key or the relative minor?  You just need to know a little bit of theory so you can pick up on the harmonic structure or be knowledgeable about the use of melodic minors and harmonic minor variants that will usually throw in a few tell tale accidentals to clue you in.  Ie., if you think you are either in Eb or Cm - and you see a lot of B naturals... hint hint - you are almost certainly in Cm.