how to emulate insert ignore and on duplicate key update sql merge with postgresql

Question

Some SQL servers have a feature where INSERT is skipped if it would violate a primary unique key constraint  For instance  MySQL has INSERT IGNORE   What s the best way to emulate INSERT IGNORE and ON DUPLICATE KEY UPDATE with PostgreSQL

User · Answer

For data import scripts  to replace  IF NOT EXISTS   in a way  there s a slightly awkward formulation that nevertheless works   DO  do  BEGIN PERFORM id FROM whatever table   IF NOT FOUND THEN -- INSERT stuff END IF  END  do

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For those of you that have Postgres 9 5 or higher  the new ON CONFLICT DO NOTHING syntax should work   INSERT INTO target table  field one  field two  field three    SELECT field one  field two  field three FROM source table ON CONFLICT  field one  DO NOTHING    For those of us who have an earlier version  this right join will work instead   INSERT INTO target table  field one  field two  field three   SELECT source table field one  source table field two  source table field three FROM source table  LEFT JOIN target table ON source table field one   target table field one WHERE target table field one IS NULL

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On bulk  you can always delete the row before the insert  A deletion of a row that doesn t exist doesn t cause an error  so its safely skipped

User · Answer

Try to do an UPDATE  If it doesn t modify any row that means it didn t exist  so do an insert  Obviously  you do this inside a transaction   You can of course wrap this in a function if you don t want to put the extra code on the client side  You also need a loop for the very rare race condition in that thinking    There s an example of this in the documentation  http   www postgresql org docs 9 3 static plpgsql-control-structures html  example 40-2 right at the bottom   That s usually the easiest way  You can do some magic with rules  but it s likely going to be a lot messier  I d recommend the wrap-in-function approach over that any day   This works for single row  or few row  values  If you re dealing with large amounts of rows for example from a subquery  you re best of splitting it into two queries  one for INSERT and one for UPDATE  as an appropriate join subselect of course - no need to write your main filter twice

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INSERT INTO mytable col1 col2       SELECT  val1   val2       WHERE NOT EXISTS  SELECT 1 FROM mytable WHERE col1  val1

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As  hanmari mentioned in his comment  when inserting into a postgres tables  the on conflict      do nothing is the best code to use for not inserting duplicate data    query    INSERT INTO db table name column name           VALUES  s  ON CONFLICT  column name  DO NOTHING     The ON CONFLICT line of code will allow the insert statement to still insert rows of data  The query and values code is an example of inserted date from a Excel into a postgres db table  I have constraints added to a postgres table I use to make sure the ID field is unique  Instead of running a delete on rows of data that is the same  I add a line of sql code that renumbers the ID column starting at 1  Example   q    ALTER id column serial RESTART WITH 1    If my data has an ID field  I do not use this as the primary ID serial ID  I create a ID column and I set it to serial  I hope this information is helpful to everyone   I have no college degree in software development coding  Everything I know in coding  I study on my own

User · Answer

To get the insert ignore logic you can do something like below  I found simply inserting from a select statement of literal values worked best  then you can mask out the duplicate keys with a NOT EXISTS clause  To get the update on duplicate logic I suspect a pl pgsql loop would be necessary   INSERT INTO manager vin manufacturer  SELECT   FROM  VALUES     935    Citro  n Brazil   Citro  n        ABC    Toyota    Toyota        ZOM    OM   OM       as tmp  vin manufacturer id  manufacturer desc  make desc    WHERE NOT EXISTS       --ignore anything that has already been inserted     SELECT 1 FROM manager vin manufacturer m where m vin manufacturer id   tmp vin manufacturer id

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Looks like PostgreSQL supports a schema object called a rule   http   www postgresql org docs current static rules-update html  You could create a rule ON INSERT for a given table  making it do NOTHING if a row exists with the given primary key value  or else making it do an UPDATE instead of the INSERT if a row exists with the given primary key value   I haven t tried this myself  so I can t speak from experience or offer an example

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This solution avoids using rules   BEGIN    INSERT INTO tableA  unique column c2 c3  VALUES  1 2 3   EXCEPTION     WHEN unique violation THEN      UPDATE tableA SET c2   2  c3   3 WHERE unique column   1  END    but it has a performance drawback  see PostgreSQL org       A block containing an EXCEPTION clause is significantly more expensive   to enter and exit than a block without one  Therefore  don t use   EXCEPTION without need

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With PostgreSQL 9 5  this is now native functionality  like MySQL has had for several years       INSERT     ON CONFLICT DO NOTHING UPDATE   UPSERT        9 5 brings support for  UPSERT  operations    INSERT is extended to accept an ON CONFLICT DO UPDATE IGNORE clause  This clause specifies an alternative action to take in the event of a would-be duplicate violation            Further example of new syntax      INSERT INTO user logins  username  logins  VALUES   Naomi  1    James  1   ON CONFLICT  username  DO UPDATE SET logins   user logins logins   EXCLUDED logins

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Edit  in case you missed warren s answer  PG9 5 now has this natively  time to upgrade     Building on Bill Karwin s answer  to spell out what a rule based approach would look like  transferring from another schema in the same DB  and with a multi-column primary key    CREATE RULE  my table on duplicate ignore  AS ON INSERT TO  my table    WHERE EXISTS SELECT 1 FROM my table                  WHERE  pk col 1  pk col 2   NEW pk col 1  NEW pk col 2     DO INSTEAD NOTHING  INSERT INTO my table SELECT   FROM another schema my table WHERE some cond  DROP RULE  my table on duplicate ignore  ON  my table     Note  The rule applies to all INSERT operations until the rule is dropped  so not quite ad hoc

[database] how to emulate "insert ignore" and "on duplicate key update" (sql merge) with postgresql?

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