How to merge duplicate lines into same row with primary key and more than one column of information

Could you please try following. Written and tested with shown samples in GNU awk.

awk '
BEGIN{
  FS=","
  OFS="|"
}
FNR==NR{
  first=$1
  $1=""
  sub(/^,/,"")
  arr[first]=(first in arr?arr[first] OFS:"")$0
  next
}
($1 in arr){
  print $1 arr[$1]
  delete arr[$1]
}
' Input_file  Input_file

Explanation: Adding detailed explanation for above.

awk '                       ##Starting awk program from here.
BEGIN{                      ##Starting BEGIN section of this program from here.
  FS=","                    ##Setting FS as comma here.
  OFS="|"                   ##Setting OFS as | here.
}
FNR==NR{                    ##Checking FNR==NR which will be TRUE when first time Input_file is being read.
  first=$1                  ##Setting first as 1st field here.
  $1=""                     ##Nullifying first field here.
  sub(/^,/,"")              ##Substituting starting comma with NULL in current line.
  arr[first]=(first in arr?arr[first] OFS:"")$0  ##Creating arr with index of first and keep adding same index value to it.
  next                      ##next will skip all further statements from here.
}
($1 in arr){                ##Checking condition if 1st field is present in arr then do following.
  print $1 arr[$1]          ##Printing 1st field with arr value here.
  delete arr[$1]            ##Deleting arr item here.
}
' Input_file  Input_file    ##Mentioning Input_file names here.

Another awk:

$ awk '
BEGIN {               # set them field separators
    FS=","
    OFS="|"
}
{
    if($1 in a) {     # if $1 already has an entry in a hash
        t=$1          # store key temporarily
        $1=a[$1]      # set the a hash entry to $1
        a[t]=$0       # and hash the record
    } else {          # if $1 seen for the first time
        $1=$1         # rebuild record to change the separators
        a[$1]=$0      # and hash the record
    }
}
END {                 # afterwards
    for(i in a)       # iterate a 
        print a[i]    # and output
}' file