MySQL in a Nutshell, 2nd Edition

Name

REPLACE

Synopsis

REPLACE [LOW_PRIORITY|DELAYED] [INTO] table [(column,...)]
  VALUES ({expression|DEFAULT},...)[, (...)]

REPLACE [LOW_PRIORITY|DELAYED] [INTO] table
  SET column={expression|DEFAULT}[, ...]

REPLACE [LOW_PRIORITY|DELAYED] [INTO] table [(column,...)]
  SELECT...

Use this statement to insert new rows of data and to replace existing rows where the PRIMARY KEY or UNIQUE index key is the same as the new record being inserted. This statement requires INSERT and DELETE privileges because it is potentially a combination of both.

The LOW_PRIORITY keyword instructs the server to wait until there are no queries on the table named, including reads, and then to lock the table for exclusive use by the thread so that data may be inserted and replaced. When the statement is finished, the lock is released, automatically. For busy servers, a client may be waiting for quite a while. The DELAYED keyword will free the client by storing the statement in a buffer for processing when the table is not busy. The client won’t be given notice of the success of the statement, just that it’s buffered. If the server crashes before the changes to the data are processed, the client will not be informed and the buffer contents will be lost. The INTO keyword is optional and is a matter of style preference and compatibility with other database engines.

The REPLACE statement has three basic formats. The first contains the values for each row in parentheses after the VALUES keyword. If the order and number ...