![]() The primary key for the Country table is ID.įor example, the current row that we replace in the table is shown below. It becomes equivalent to INSERT, because there is no index to be used to determine whether a new row is duplicate to another existing row. ![]() Note that unless the table has a PRIMARY KEY or a UNIQUE constraint, using a REPLACE statement makes no sense. | ID | int | NO | PRI | NULL | auto_increment | | Field | Type | Null | Key | Default | Extra | In this example, we will replace a current row of data in the Country table from the world MySQL database. We cannot refer to values from the current row and use them in the new row. Any missing columns are set to their default values, just like in the INSERT statement. The values for all the columns are taken from the values specified in the REPLACE statement. Mysql> REPLACE INTO table_name (column_list) VALUES(values_list) The REPLACE statement uses the following syntax: The INSERT statement fails because a duplicate-key error occurs for a primary key or unique constraint if the column has the same value for new row and existing old row. REPLACE works like INSERT, except that if an old row in the table has the same value as a new row for a PRIMARY KEY or UNIQUE constraint, the old row is deleted before the new row is inserted. The statement either inserts or deletes and inserts rows. The REPLACE statement is a MySQL extension to the SQL standard. If you are using REPLACE INTO.In this tutorial, we will learn about MySQL REPLACE statement. We did not realize this and had the triggers that should be triggered on DELETE triggered.Īfter checking all the code, we just found a script that does a replace to refresh the values of some fields. PLEASE Note that the REPLACE does a DELETE operation. Mysql> REPLACE DELAYED INTO `online_users` SET `session_id`='3580cc4e61117c0785372c426eddd11c', `user_id` = 'XXX', `page` = '/', `lastview` = NOW() ĮRROR 1031 (HY000): Table storage engine for 'online_users' doesn't have this option INNODB mysql 5.0 does not support "DELAYED" but does support LOW_PRIORITY : as an alternative if you're willing to stick to MySQL 4.1+ If you're looking at a single unique column table (Primary Key), please use UPDATE, or INSERT. Then REPLACE INTO becomes more efficient from DELETE FROM. The only time when I can see where you'd actually need a REPLACE INTO is when you have multiple unique constraints on a table, and need to drop any rows that would match any of the constraints. There's a lot of management of rows involved in this, and if you're doing it frequently, you'll hurt your performance unless you simply cannot do with any other syntax. Keep in mind that a REPLACE INTO requires a test on the keys, and if a matching unique key is found on any or all columns, a DELETE FROM is executed, then an INSERT is executed. ![]() Please note that REPLACE INTO is a much slower performer than an UPDATE statement. It is best to avoid REPLACE when working with constraints.īe careful with REPLACE INTO with server side prepared statements and the 3.1.6 driver - it doesn't support them. => F is truncated - not the desired effect. `id` int(10) unsigned NOT NULL auto_increment,ĬONSTRAINT `fkey` FOREIGN KEY (`foreign_id`) REFERENCES `T` (`id`) ON DELETE If you run a replace on existing keys on table T, and table F references T with a forgein key constraint ON DELETE CASCADE, then table T will be updated - but table F will be emptied due to the DELETE before INSERT. User Comments Posted by no forms on Octo12:16pmīe careful with InnoDB tables and REPLACE: If you are using the C API, the affected-rows count can beĬurrently, you cannot replace into a table and select from the It also replaced any rows: Check whether the count is 1 (added) or The affected-rows count makes it easy to determine whether It is possibleįor a single row to replace more than one old row if the tableĬontains multiple unique indexes and the new row duplicates valuesįor different old rows in different unique indexes. Rows were deleted before the new row was inserted. If the count is greater than 1, one or more old To the column name on the right hand side is treated asĬount to indicate the number of rows affected. Values for all columns are taken from the values specified in theĬolumns are set to their default values, just as happens forįrom the current row and use them in the new row. Note that unless the table has a PRIMARY KEY orīecause there is no index to be used to determine whether a new For another MySQL extension to standard SQL. ![]() It either inserts, or deletesĪnd inserts. Index, the old row is deleted before the new row is inserted. In the table has the same value as a new row for a ![]()
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