(1062) Duplicate entry '' for key '*UNKNOWN*' (3 replies)

Hi all,

I recently encounter the "(1062) Duplicate entry '' for key '*UNKNOWN*'" error with the following SQL. It is strange that none of the updating value is '', and why is the key *UNKNOWN* ???

Please help.

1) (1062) Duplicate entry '' for key '*UNKNOWN*'
UPDATE common_task SET applicants=applicants+'1' WHERE taskid=5

2) (1062) Duplicate entry '' for key '*UNKNOWN*'
UPDATE common_task SET achievers=achievers+'1' WHERE taskid=10

3) (1062) Duplicate entry '' for key '*UNKNOWN*'
INSERT INTO forum_medallog SET `uid`='6042' , `medalid`='36' , `type`='0' , `dateline`='1407142477' , `expiration`='0' , `status`='0'

4) (1062) Duplicate entry '' for key '*UNKNOWN*'
REPLACE INTO common_mytask SET `uid`='490' , `username`='1ed87718-2e5a-4d3d-b120-5fcffcc9193b' , `taskid`='4' , `csc`='0\\t1407140796' , `dateline`='1407140796'

5) (1062) Duplicate entry '' for key '*UNKNOWN*'
UPDATE common_member_count SET `extcredits1`=`extcredits1`+'2',`posts`=`posts`+'1' WHERE uid IN ('4820')

6) (1062) Duplicate entry '' for key '*UNKNOWN*'
UPDATE common_mytask SET `status`='1' , `csc`='100' , `dateline`='1407139450' WHERE `uid`='4701' AND `taskid`='7'