REPLACE

REPLACE [LOW_PRIORITY]
[INTO] tbl_name
[PARTITION (partition_name,...)]
[(col_name,...)]
{VALUES | VALUE} ({expr | DEFAULT},...),(...),...
REPLACE [LOW_PRIORITY]
[INTO] tbl_name
[PARTITION (partition_name,...)]
SET col_name={expr | DEFAULT}, ...
REPLACE [LOW_PRIORITY]
[INTO] tbl_name
[PARTITION (partition_name,...)] 
[(col_name,...)]
SELECT ...
REPLACE is the same as INSERT, except that when there is a duplicate value for a PRIMARY KEY or a UNIQUE index, the old row is deleted before the insertion.
A REPLACE statement returns the sum of the rows deleted and inserted.