using find
should do the work.
*/1 * * * * find /tmp/ -maxdepth 1 -type f -name '#sql_*.MYD' -empty -delete
-maxdepth 1
: do not find file in subdirectory
-type f
: matches only regular file (no directory, no symbolic link, and so on)
-name <pattern>
: matches the file name pattern
-empty
: matches only empty file
-delete
: delete that file
see man find
for detail.