While executing an INSERT statement with many rows, I want to skip duplicate entries that would otherwise cause failure. After some research, my options appear to be the use of either:
ON DUPLICATE KEY UPDATE which implies an unnecessary update at some cost, orINSERT IGNORE implies an invitation for other kinds of failure to slip in unannounced.Am I right in these assumptions? What's the best way to simply skip the rows that might cause duplicates and just continue on to the other rows?
I would recommend using INSERT...ON DUPLICATE KEY UPDATE.
If you use INSERT IGNORE, then the row won't actually be inserted if it results in a duplicate key. But the statement won't generate an error. It generates a warning instead. These cases include:
PRIMARY KEY or UNIQUE constraints.NOT NULL constraint.If you use REPLACE, MySQL actually does a DELETE followed by an INSERT internally, which has some unexpected side effects:
REPLACE.DELETE are executed unnecessarily.correction: both REPLACE and INSERT...ON DUPLICATE KEY UPDATE are non-standard, proprietary inventions specific to MySQL. ANSI SQL 2003 defines a MERGE statement that can solve the same need (and more). MySQL does not support the MERGE statement, even though this feature has been requested since 2005.
A user tried to edit this post (the edit was rejected by moderators). The edit tried to add a claim that INSERT...ON DUPLICATE KEY UPDATE causes a new auto-increment id to be allocated. It's true that the new id is generated, but it is not used in the changed row.
See demonstration below, tested with Percona Server 5.5.28. The configuration variable innodb_autoinc_lock_mode=1 (the default):
mysql> create table foo (id serial primary key, u int, unique key (u)); mysql> insert into foo (u) values (10); mysql> select * from foo; +----+------+ | id | u | +----+------+ | 1 | 10 | +----+------+ mysql> show create table foo\G CREATE TABLE `foo` ( `id` bigint(20) unsigned NOT NULL AUTO_INCREMENT, `u` int(11) DEFAULT NULL, PRIMARY KEY (`id`), UNIQUE KEY `u` (`u`) ) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=latin1 mysql> insert into foo (u) values (10) on duplicate key update u = 20; mysql> select * from foo; +----+------+ | id | u | +----+------+ | 1 | 20 | +----+------+ mysql> show create table foo\G CREATE TABLE `foo` ( `id` bigint(20) unsigned NOT NULL AUTO_INCREMENT, `u` int(11) DEFAULT NULL, PRIMARY KEY (`id`), UNIQUE KEY `u` (`u`) ) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=latin1 The above demonstrates that the IODKU statement detects the duplicate, and invokes the update to change the value of u. Note the AUTO_INCREMENT=3 indicates an id was generated, but not used in the row.
Whereas REPLACE does delete the original row and inserts a new row, generating and storing a new auto-increment id:
mysql> select * from foo; +----+------+ | id | u | +----+------+ | 1 | 20 | +----+------+ mysql> replace into foo (u) values (20); mysql> select * from foo; +----+------+ | id | u | +----+------+ | 3 | 20 | +----+------+ 
INSERT IGNORE also increments the auto-increment value, even when it does not insert anything.INSERT IGNORE can also increments the auto-increment value when the insertion fails on other reason than the same key, e.g. if the value u must be unique
In case you want to see what this all means, here is a blow-by-blow of everything:
CREATE TABLE `users_partners` ( `uid` int(11) NOT NULL DEFAULT '0', `pid` int(11) NOT NULL DEFAULT '0', PRIMARY KEY (`uid`,`pid`), KEY `partner_user` (`pid`,`uid`) ) ENGINE=MyISAM DEFAULT CHARSET=utf8 The primary key is based on both columns of this quick reference table. A Primary key requires unique values.
Let's begin:
INSERT INTO users_partners (uid,pid) VALUES (1,1); ...1 row(s) affected INSERT INTO users_partners (uid,pid) VALUES (1,1); ...Error Code : 1062 ...Duplicate entry '1-1' for key 'PRIMARY' INSERT IGNORE INTO users_partners (uid,pid) VALUES (1,1); ...0 row(s) affected INSERT INTO users_partners (uid,pid) VALUES (1,1) ON DUPLICATE KEY UPDATE uid=uid ...0 row(s) affected note, the above saved too much extra work by setting the column equal to itself, no update actually needed
REPLACE INTO users_partners (uid,pid) VALUES (1,1) ...2 row(s) affected and now some multiple row tests:
INSERT INTO users_partners (uid,pid) VALUES (1,1),(1,2),(1,3),(1,4) ...Error Code : 1062 ...Duplicate entry '1-1' for key 'PRIMARY' INSERT IGNORE INTO users_partners (uid,pid) VALUES (1,1),(1,2),(1,3),(1,4) ...3 row(s) affected no other messages were generated in the console, and it now has those 4 values in the table data. I deleted everything except (1,1) so I could test from the same playing field
INSERT INTO users_partners (uid,pid) VALUES (1,1),(1,2),(1,3),(1,4) ON DUPLICATE KEY UPDATE uid=uid ...3 row(s) affected REPLACE INTO users_partners (uid,pid) VALUES (1,1),(1,2),(1,3),(1,4) ...5 row(s) affected So there you have it. Since this was all performed on a fresh table with nearly no data and not in production, the times for execution were microscopic and irrelevant. Anyone with real-world data would be more than welcome to contribute it.
Something important to add: When using INSERT IGNORE and you do have key violations, MySQL does NOT raise a warning!
If you try for instance to insert 100 records at a time, with one faulty one, you would get in interactive mode:
Query OK, 99 rows affected (0.04 sec)
Records: 100 Duplicates: 1 Warnings: 0
As you see: No Warnings! This behavior is even wrongly described in the official Mysql Documentation.
If your script needs to be informed, if some records have not been added (due to key violations) you have to call mysql_info() and parse it for the "Duplicates" value.
mysqli_affected_rows() to know if the INSERT actually happened.
Cannot add or update a child row: a foreign key constraint fails and no rows (even valid ones) are added.
INSERT IGNORE, duplicate keys are ignored with no error or warning.
I routinely use INSERT IGNORE, and it sounds like exactly the kind of behavior you're looking for as well. As long as you know that rows which would cause index conflicts will not be inserted and you plan your program accordingly, it shouldn't cause any trouble.
As mentioned above, if you use INSERT..IGNORE, errors that occur while executing the INSERT statement are treated as warnings instead.
One thing which is not explicitly mentioned is that INSERT..IGNORE will cause invalid values will be adjusted to the closest values when inserted (whereas invalid values would cause the query to abort if the IGNORE keyword was not used).
Replace Into seems like an option. Or you can check with
IF NOT EXISTS(QUERY) Then INSERT This will insert or delete then insert. I tend to go for a IF NOT EXISTS check first.
Potential danger of INSERT IGNORE. If you are trying to insert VARCHAR value longer then column was defined with - the value will be truncated and inserted EVEN IF strict mode is enabled.
Adding to this. If you use both INSERT IGNORE and ON DUPLICATE KEY UPDATE in the same statement, the update will still happen if the insert finds a duplicate key. In other words, the update takes precedence over the ignore. However, if the ON DUPLICATE KEY UPDATE clause itself causes a duplicate key error, that error will be ignored.
This can happen if you have more than one unique key, or if your update attempts to violate a foreign key constraint.
CREATE TABLE test (id BIGINT (20) UNSIGNED AUTO_INCREMENT, str VARCHAR(20), PRIMARY KEY(id), UNIQUE(str)); INSERT INTO test (str) VALUES('A'),('B'); /* duplicate key error caused not by the insert, but by the update: */ INSERT INTO test (str) VALUES('B') ON DUPLICATE KEY UPDATE str='A'; /* duplicate key error is suppressed */ INSERT IGNORE INTO test (str) VALUES('B') ON DUPLICATE KEY UPDATE str='A';If using insert ignore having a SHOW WARNINGS; statement at the end of your query set will show a table with all the warnings, including which IDs were the duplicates.
SHOW WARNINGS; only seems to affect the latest query. Any previous statements are not accumulated, if you have more than a single statement.INSERT...ON DUPLICATE KEY UPDATE is prefered to prevent unexpected Exceptions management.
In my case I know that col1 and col2 make a unique composite index.
It keeps track of the error, but does not throw an exception on duplicate. Regarding the performance, the update by the same value is efficient as MySQL notices this and does not update it
INSERT INTO table (col1, col2, col3, col4) VALUES (?, ?, ?, ?) ON DUPLICATE KEY UPDATE col1 = VALUES(col1), col2 = VALUES(col2) The idea to use this approach came from the comments at phpdelusions.net/pdo.
INSERT as clean as possible. First query, SELECT and filter the data from another table and then INSERT. Hope this helpIf you want to insert in the table and on the conflict of the primary key or unique index it will update the conflicting row instead of inserting that row.
Syntax:
insert into table1 set column1 = a, column2 = b on duplicate update column2 = c; Now here, this insert statement may look different what you have seen earlier. This insert statement trying to insert a row in table1 with the value of a and b into column column1 and column2 respectively.
Let's understand this statement in depth:
For example: here column1 is defined as the primary key in table1.
Now if in table1 there is no row having the value “a” in column1. So this statement will insert a row in the table1.
Now if in table1 there is a row having the value “a” in column2. So this statement will update the row’s column2 value with “c” where the column1 value is “a”.
So if you want to insert a new row otherwise update that row on the conflict of the primary key or unique index.
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