Concatenating values from a single column to remove duplicates in another.

Hello,

I am trying to combine columns so I can get rid of the duplicate values in COLUMNA, and concatenate the corresponding values in COLUMNB with a "; " separating them. I was wondering what kind of formula I would need to do so.

What I have:

   COLUMNA    |   COLUMNB   
   11111111   |   ASDFASD   
   11111112   |   AAAAAAA
   11111113   |   QWERTY   
   11111113   |   QAZWSX
   11111113   |   ZXCVBNM

What I need the final result to be:

   COLUMNA    |   COLUMNB   
   11111111   |   ASDFASD
   11111112   |   AAAAAAA
   11111113   |   QWERTY; QAZWSX; ZXCVBNM

I have a worksheet of over 1,000 values, and about half of them contain duplicate COLUMNA values.

I hope I was descriptive enough, let me know if you have questions regarding my examples.

Thank you!