PostgresDB 42P21: Collation Mismatch

Mismatch in collation settings.

When encountering the error 42P21: Collation Mismatch in PostgreSQL, follow these immediate actions for investigation:

  1. Check the collations of the databases involved in the operation. Run this query to find the default collation of your database and compare it with others if necessary:
  2. SELECT datcollate FROM pg_database WHERE datname = 'your_database_name';
  3. Identify the collations of the columns involved in the operation that caused the error. Use this query, adjusting it to your specific table and column names:
  4. SELECT column_name, collation_name FROM information_schema.columns WHERE table_name = 'your_table_name';
  5. If a specific operation (like a JOIN or UNION) triggered the error, examine the collations of all involved columns or databases to ensure they match. This might require running the above queries for each involved table or database.
  6. To resolve the mismatch, you may need to explicitly set the collation for the operation. This can be done by using the COLLATE clause in your SQL query. For example, if you're comparing two columns with different collations, you can explicitly set the collation for the operation:
  7. SELECT * FROM table1 t1 JOIN table2 t2 ON t1.text_column COLLATE "en_US" = t2.text_column COLLATE "en_US";

Replace "en_US" with the appropriate collation that matches across your operations. Note that changing column or database collation might involve deeper changes and should be approached with caution.

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