SQL Dialects Reference/Write queries/Replace query

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[edit] Replace query

Replace query inserts new row if no row with such primary key exists or updates existing row if it does. SQL:2003 standard introduced a MERGE statement to implement such functionality, while other implementations provide similar queries named "REPLACE" or so-called "Upsert" query (a portmanteau of UPDATE and INSERT).

• Standard. MERGE statement can be used to do a replace query:

MERGE INTO table_name1 USING table_name2 ON (condition)
WHEN MATCHED THEN UPDATE SET column1 = value1 [, column2 = value2 ...]
WHEN NOT MATCHED THEN INSERT columns VALUES (values) 

Note that MERGE is much more powerful than just doing replace queries.

• DB2: MERGE statement

MERGE INTO phonebook AS p
   USING ( VALUES ('john doe', '1234' ) ) AS v(name, extension)
   ON ( p.name = v.name )
   WHEN MATCHED
      UPDATE SET p.extension = v.extension
   WHEN NOT MATCHED
      INSERT VALUES ( v.name, v.extension )

• MySQL: Allows 3 syntaxes: non-standard REPLACE query, (since 4.1) INSERT ... ON DUPLICATE KEY UPDATE, and a variant on IF EXISTS.

REPLACE [INTO] table [(columns)] VALUES (values)

INSERT INTO table (columns) VALUES (values) ON DUPLICATE KEY UPDATE column1=value1, column2=value2

IF EXISTS( SELECT * FROM phonebook WHERE name = 'john doe' )
THEN UPDATE phonebook SET extension = '1234' WHERE name = 'john doe'
ELSE INSERT INTO phonebook VALUES( 'john doe','1234' )
END IF

• Oracle: MERGE statement

MERGE INTO phonebook B
USING (
  SELECT name_id
  FROM phonebook
  WHERE name = 'john doe') E
ON (B.name = E.name)
WHEN MATCHED THEN
  UPDATE SET B.extension = '1234'
WHEN NOT MATCHED THEN
  INSERT (B.name, B.extension)
  VALUES ('john doe', '1234);

• Multi-statement form:

IF EXISTS( SELECT * FROM phonebook WHERE name = 'john doe' )
UPDATE phonebook SET extension = '1234' WHERE name = 'john doe'
ELSE
INSERT INTO phonebook VALUES( 'john doe','1234' )