data set match merge, an example to study zz

The original post want to match merge A and B, and then got the result as below:

X   Y         Z               flag
1   red      brown       0
1   red      red            1
1   blue     brown       0
1   blue     red            0
3   yellow  red            0
3   yellow  pink           0
3   green   red            0
3   green   pink           0

In proc sql, it's not difficult to use inner join to merge A and B conditional on a.x = b.x. And we need to assign value to flag as if a.y matched by b.z.  At last the program can be down as:

data a;
 input x y $;
 cards;
 1 red
 1 blue
 3 yellow
 3 green
 ;
run;

data b;
 input x z $;
 cards;
 1 brown
 1 red
 2 yellow
 3 red
 3 pink
 ;
run;

proc sql;
   select a.x, a.y, b.z, case when a.y = b.z then 1 else 0 end as flag 
   from a, b
   where a.x=b.x;
quit;

***************************************************************************

 Somebody gives the solution with data step. It's pretty good, as following:

 data c;
 set a;
 do i = 1 to num;
  set b(rename = (x = x2)) nobs = num point = i;
  output;
 end;
run;

data want (drop = x2);
 set c;
 if y = z then flag = 1;
 else flag = 0;
 where x = x2;
run;

To make it clearer, here, the print of data set c is:

                                 Obs    x    y         x2    z

                                    1    1    red        1    brown
                                    2    1    red        1    red
                                    3    1    red        2    yellow
                                    4    1    red        3    red
                                    5    1    red        3    pink
                                    6    1    blue       1    brown
                                    7    1    blue       1    red
                                    8    1    blue       2    yellow
                                    9    1    blue       3    red
                                   10    1    blue       3    pink
                                   11    3    yellow     1    brown
                                   12    3    yellow     1    red
                                   13    3    yellow     2    yellow
                                   14    3    yellow     3    red
                                   15    3    yellow     3    pink
                                   16    3    green      1    brown
                                   17    3    green      1    red
                                   18    3    green      2    yellow
                                   19    3    green      3    red
                                   20    3    green      3    pink