Search through multiple table until match found

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SQL

stored-procedure

Good day!

Please help me search through multiple tables where i can find my match.

example: i have a table

Assignment_tbl and
-------------
code | desc |
1 | aaa |
2 | bbb |
3 | ccc |
-------------

Promotion_tbl
-------------
code | desc |
4 | aaa |
5 | bbb |
6 | ccc |
-------------

Want i want is to know in what table code 4 exist?
i wanted to search through assignment_tbl first if code 4 exist my query should break else if it does not exist in assignment_tbl search through promotion_tbl.

please help me. Thank you in advance.