INSERT / UPDATE to merge data, when empty data is an empty string
To avoid putting values two times in your INSERT statement use VALUES(&lt;column_name&gt;) function.


  INSERT ... ON DUPLICATE KEY UPDATE Syntax
  You can use the VALUES(col_name) function in the UPDATE clause to
  refer to column values from the INSERT portion of the INSERT ... ON
  DUPLICATE KEY UPDATE statement. In other words, VALUES(col_name) in
  the ON DUPLICATE KEY UPDATE clause refers to the value of col_name
  that would be inserted, had no duplicate-key conflict occurred. This
  function is especially useful in multiple-row inserts. The VALUES()
  function is meaningful only in INSERT ... UPDATE statements and
  returns NULL otherwise.


Unfortunately it's not very clear in your question what is your desired outcome. But assuming that you want update only columns that have NULL or empty strings you can do

INSERT INTO some_table (f_name, l_name, work)
VALUES ('Dotan', '', 'php')
ON DUPLICATE KEY UPDATE
  f_name = COALESCE(NULLIF(f_name, ''), VALUES(f_name)),
  l_name = COALESCE(NULLIF(l_name, ''), VALUES(l_name)),
  work   = COALESCE(NULLIF(work, ''), VALUES(work));


Here is SQLFiddle demo

If it's not exactly what you want, please consider to post your desired outcome and explain what values under what conditions you want to update