INSERT ... ON DUPLICATE KEY UPDATE Syntax

If you specify

ON DUPLICATE KEY UPDATE

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

UNIQUE

index or

PRIMARY KEY

, MySQL performs an

UPDATE

of the old row. For example, if column

a

is declared as

UNIQUE

and contains the value

1

, the following two statements have similar 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;

(The effects are not identical for an

InnoDB

table where

a

is an auto-increment column. With an auto-increment column, an

INSERT

statement increases the auto-increment value but

UPDATE

does not.)

The

ON DUPLICATE KEY UPDATE

clause can contain multiple column assignments, separated by commas.

With

ON DUPLICATE KEY UPDATE

, the affected-rows value per row is 1 if the row is inserted as a new row, 2 if an existing row is updated, and 0 if an existing row is set to its current values. If you specify the

CLIENT_FOUND_ROWS

flag to

mysql_real_connect()

when connecting to mysqld, the affected-rows value is 1 (not 0) if an existing row is set to its current values.

If column

b

is also unique, the

INSERT

is equivalent to this

UPDATE

statement instead:

UPDATE table SET c=c+1 WHERE a=1 OR b=2 LIMIT 1;

If

a=1 OR b=2

matches several rows, only one row is updated. In general, you should try to avoid using an

ON DUPLICATE KEY UPDATE

clause on tables with multiple unique indexes.

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;

If a table contains an

AUTO_INCREMENT

column and

INSERT ... ON DUPLICATE KEY UPDATE

inserts or updates a row, the

LAST_INSERT_ID()

function returns the

AUTO_INCREMENT

value.

The

DELAYED

option is ignored when you use

ON DUPLICATE KEY UPDATE

.

Because the results of

INSERT ... SELECT

statements depend on the ordering of rows from the

SELECT

and this order cannot always be guaranteed, it is possible when logging

INSERT ... SELECT ON DUPLICATE KEY UPDATE

statements for the master and the slave to diverge. Thus,

INSERT ... SELECT ON DUPLICATE KEY UPDATE

statements are flagged as unsafe for statement-based replication. With this change, such statements produce a warning in the log when using statement-based mode and are logged using the row-based format when using

MIXED

mode. In addition, an

INSERT ... ON DUPLICATE KEY UPDATE

statement against a table having more than one unique or primary key is also marked as unsafe. (Bug #11765650, Bug #58637) See also Section 18.2.1.1, “Advantages and Disadvantages of Statement-Based and Row-Based Replication”.

In MySQL 5.7, an

INSERT ... ON DUPLICATE KEY UPDATE

on a partitioned table using a storage engine such as

MyISAM

that employs table-level locks locks any partitions of the table in which a partitioning key column is updated. (This does not occur with tables using storage engines such as

InnoDB

that employ row-level locking.) See Section 20.6.4, “Partitioning and Locking”, for more information.

转载

INSERT ... ON DUPLICATE KEY UPDATE Syntax