How to Handle Conflicts with Multiple Unique Columns in PostgreSQL's ON CONFLICT Clause?

Specifying multiple conflict targets in PostgreSQL’s ON CONFLICT clause

PostgreSQL tables often contain multiple columns that are designated as unique. Although the ON CONFLICT clause allows conflict detection based on a single conflict target, it may be limited when managing tables with multiple unique columns.

To overcome this limitation, PostgreSQL provides a simple solution: create a unique index that spans multiple columns. By doing this, you effectively specify multiple conflict targets in the ON CONFLICT clause.

Example:

Consider a table with two unique columns col1 and col2. You can create a unique index on these two columns using the following command:

<code class="language-sql">CREATE UNIQUE INDEX idx_table_col1_col2 ON table(col1, col2);</code>

You can now leverage this index to handle conflicts involving these two columns in the ON CONFLICT clause:

<code class="language-sql">INSERT INTO table ...
ON CONFLICT (col1, col2)
DO UPDATE
SET ...</code>

When a conflict occurs, PostgreSQL will check the values ​​of col1 and col2 of the new row against the existing row to ensure uniqueness. If a conflict is detected, the DO UPDATE clause will fire, allowing you to update other columns as needed.

Note: In addition to unique indexes, PostgreSQL also supports exclusion constraints. A unique constraint prevents duplicate values ​​for a given column or set of columns, while an exclude constraint goes a step further and excludes rows that meet certain conditions. This is useful in situations where you wish to enforce more complex data integrity rules.

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