INSERT ... ON DUPLICATE KEY UPDATE Syntax

f you specify

ON DUPLICATE KEY UPDATE

,
and a
row is inserted that would cause a duplicate value in a

UNIQUE

index or

PRIMARY
KEY

, an

UPDATE

of the
old row is performed. For example, if column

a

is declared as

UNIQUE

and contains the value

1

, the
following two
statements have identical effect:

INSERT INTO table (a,b,c) VALUES (1,2,3)

ON DUPLICATE KEY UPDATE c=c+1;

UPDATE table SET c=c+1 WHERE a=1;

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. Example:INSERT INTO table (a,b,c) VALUES (1,2,3),(4,5,6)
ON DUPLICATE KEY UPDATE c=VALUES(a)+VALUES(b);That statement is identical to the following two statements:INSERT INTO table (a,b,c) VALUES (1,2,3)
ON DUPLICATE KEY UPDATE c=3;
INSERT INTO table (a,b,c) VALUES (4,5,6)
ON DUPLICATE KEY UPDATE c=9;