SELECT t.*
  FROM YOUR_TABLE t
 WHERE t.column LIKE '123-%'
    OR t.column LIKE '123_%'

SELECT a.*
  FROM YOUR_TABLE a
 WHERE a.column LIKE '123-%'
UNION ALL
SELECT b.*
  FROM YOUR_TABLE b
 WHERE b.column LIKE '123_%'

select * from foo where bar regexp '^123-|_'

SELECT * FROM table
  WHERE field like "123"
    OR field LIKE "123-%"
    OR field like "123_%";

select * from table where field regexp '^[1-9]{3}[_-]';