Transmogrify into date from multiple columns

Question

What is a better way to program the following SQL:

str_to_date(
  concat(convert(D.DAY, CHAR(2)),
  '-',
  convert(M.MONTH, CHAR(2)),
  '-',
  convert(M.YEAR, CHAR(4))),
  '%e-%m-%Y' ) as AMOUNT_DATE

I want to convert the columns D.DAY, M.MONTH, and M.YEAR to a date field using MySQL. The above works, but seems much more complicated than it needs to be. (If there's an ANSI SQL way to do it, that would be even better.)

Thank you!

Answer 1

What about

DATE_ADD(
  DATE_ADD(
    MAKEDATE(M.YEAR,1),
    INTERVAL M.MONTH-1 MONTH
  ), 
  INTERVAL D.DAY-1 DAY
)

Answer 2

One small improvement you can make is using CONCAT_WS instead of CONCAT (the "WS" stands for "with separator"--it's the equivalent of join or implode in other languages). And MySQL should automatically convert the arguments to strings, so the CONVERT functions are, I believe, unnecessary.

STR_TO_DATE(
  CONCAT_WS('-', D.DAY, M.MONTH, M.YEAR),
  '%e-%m-%Y'
) AS AMOUNT_DATE

I'm guessing this doesn't perform as well as Tomalak's arithmetic solution, though.