Array of arrays works well. Build a line of table_3 (using array slices) when a match is found.

use strict;
use warnings;
use Data::Dumper;
my @table_1 = (
    # A  B  C
    [ 1, 1, 1 ],
    [ 1, 0, 2 ],
    [ 0, 1, 3 ],
);
my @table_2 = (
    # A  P  Q  R
    [ 1, 1, 0, 1 ],
    [ 1, 0, 1, 0 ],
    [ 0, 0, 0, 1,],
);

my @table_3;
foreach my $row_of_1 (@table_1) {
    foreach  my $row_of_2 (@table_2) {
        if ( $row_of_1->[0] == $row_of_2->[0] ) {
            push @table_3, [@{$row_of_1}[1..2],@{$row_of_2}[1..3]];
        }
    }
}

print Dumper \@table_3;
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