Use multiple conflict_target in ON CONFLICT clause

Advanced conflict handling with exclusion constraints

Exclusion constraints provide advanced tools for managing complex conflict scenarios. They excel at preventing overlapping time periods, which are as unwelcome as pineapple on pizza to some SQL practitioners.

Example of an exclusion constraint:

CREATE EXTENSION IF NOT EXISTS btree_gist;  // Just in case, because everyone loves options!

ALTER TABLE my_table ADD CONSTRAINT no_overlap EXCLUDE USING gist (
  col1 WITH =,
  tsrange(start_time, end_time) WITH &&
);
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So unlike that pineapple pizza, the above code ensures no two rows can have the same col1 and overlapping time periods - talk about having your pizza and eating it without overlapping toppings!

Handling complex cases with stored procedures and EXCEPTION handling

In navigating the sea of conflicts, sometimes unique or exclusion constraints are like rafts when you need a ship. In those cases, stored procedures with EXCEPTION handling come to the rescue like a SQL-made battleship.

Example of a stored procedure with EXCEPTION:

CREATE OR REPLACE FUNCTION upsert_my_table(
  key1 INT, key2 INT, data TEXT
) RETURNS VOID AS $$
BEGIN
  LOOP
    -- Knock, knock! Update existing row, are you there?
    UPDATE my_table SET col3 = data WHERE col1 = key1 AND col2 = key2;
    IF found THEN
      -- Row found, mission accomplished!
      RETURN;
    END IF;
    -- Nobody home! Moving on to plan B: insert a new row
    BEGIN
      INSERT INTO my_table (col1, col2, col3) VALUES (key1, key2, data);
      -- Yes, that's right, we called dibs on this row.
      RETURN;
    EXCEPTION WHEN unique_violation THEN
      -- Ah, the thrill of encountering a unique_violation exception!
      -- As cool programmers say: "When life gives you exceptions, just loop!"
    END;
  END LOOP;
END;
$$ LANGUAGE plpgsql;


Just like an endless loop of good movies on a rainy day, the loop in this procedure handles uniqueness violations by giving them a second airing, setting the stage for more graceful recovery.

The limitation: PostgreSQL's ON CONFLICT

As of PostgreSQL 9.5, the ON CONFLICT clause doesn't perform a breakdance with multiple conflict_targets. This leads us to seek creative solutions that are more creative than salsa dancing on a keyboard.

• Looping in stored functions: Like binging on your favorite series, looping lets you sequentially attempt different resolutions until you fall asleep on the keyboard—or resolve the conflict.
• Partial unique indexes: These indexes let you enforce uniqueness like a selective bouncer in a classy nightclub—only for rows that meet the conditions and dress code.
• Triggers and custom functions: As in super-hero team-ups, our mighty duo can craft custom logic for conflict resolution, only with less ground-shattering fights.

Optimal table configuration via refactoring

In times of reoccurring conflict resolution challenges, consider a reconstruction of your table. If you're fighting with conflicting data more than you chew on your pizza, create a single column that combines both these conflicting entities into a hashed or concatenated value. This could be indexed upon with a unique constraint, faster than you can say "Cowabunga!"

Exploit partial unique indexes

If conflicts tend to depend on certain conditions, partial unique indexes act like your personal Swiss army knife. These friendly tools allow you to enforce uniqueness only when specific conditions are met. This is flexibility paired with the performance of Usain Bolt sprinting after pizza delivery.

Example of a partial unique index:

CREATE UNIQUE INDEX idx_unique_active ON my_table (col1, col2)
WHERE is_active = TRUE;


This index is like the friend who only keeps an eye on active records and lets the remainder do whatever, resulting in an unconstrained hangout!

Up-to-date with PostgreSQL updates

Track updates to PostgreSQL because you never know when they will introduce a more accommodating guest house for the ON CONFLICT clause. Future versions might bring more sophisticated conflict-avoiding strategies to the table, just like your aunt brings more dishes to the family dinner.