How to merge two tables using SAS proc sql

Here is the exam data table that I would like to process here:

-origin data

–a table

STU_ID STU_KEY STU_CODE_1
123 2002123 A121
124 2002124 A122
125 2002125 A123
126 2002126 A124

–b table |STU_ID|STU_KEY|STU_CODE_2| |——|——-|———-| |123 |2002223|B121 | |124 |2002224|B122 | |125 |2002225|C123 | |126 |2002226|C124 | |127 |2002127|C125 |

I want to merge between ‘a’ and ‘b’ tables using code of SAS proc sql as follows.

-result data merge table

STU_ID STU_KEY STU_CODE_1 STU_CODE_2
123 2002123 A121
123 2002223 B121
124 2002124 A122
124 2002224 B122
125 2002125 A123
125 2002225 C123
126 2002126 A124
126 2002226 C124
127 2002127 C125
 '''error code'''
 PROC SQL;
 CREATE TABLE a_b_merge as
 SELECT t1.STU_ID, 
        t1.STU_KEY, 
        t1.STU_CODE_1
        t2.STU_CODE_2
 FROM a as t1 full join b as t2
 ON t1.STU_ID=t2.STU_ID
 QUIT;  

Let me know how to solve this problem.