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Description

This error indicates that two or more values being compared or operated upon have conflicting collation settings, preventing a direct comparison or operation. It typically arises when character strings are involved in expressions, joins, or function calls across different collations.

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Error Message

collation mismatch

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Known Causes

4 known causes

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Conflicting Column Collations

Occurs when comparing or joining columns that have been defined with different character collations, leading to an ambiguous sort order or comparison rule.

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Literal String Collation Mismatch

Arises when a string literal used in a query has an implicit collation that differs from the collation of the column or expression it's being compared against.

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Function Argument Collation Inconsistency

Some string manipulation or comparison functions require all their text arguments to have compatible collations. This error occurs if they do not.

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Database or Table Collation Differences

Operations involving data from different databases or schemas within the same database, where the underlying collation settings for character data types diverge.

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Solutions

4 solutions available

1. Explicitly Specify Collation During Table Creation easy

Define the collation for specific columns or the entire table when creating it to avoid future mismatches.

1

When creating a new table, explicitly define the `COLLATE` clause for text-based columns that require a specific collation. If you want the entire table to use a specific collation, you can define it at the table level.

CREATE TABLE my_table (
    id SERIAL PRIMARY KEY,
    name VARCHAR(100) COLLATE "en_US.UTF-8",
    description TEXT COLLATE "C"
);

2

Alternatively, define a default collation for the entire table.

CREATE TABLE another_table (
    id SERIAL PRIMARY KEY,
    name VARCHAR(100),
    description TEXT
) COLLATE "en_GB.UTF-8";

2. Alter Existing Columns to Match Target Collation medium

Modify the collation of existing columns in a table to align with the desired or expected collation.

1

Identify the columns causing the collation mismatch. You can do this by examining the error message or by querying the `pg_attribute` and `pg_collation` system catalogs.

SELECT a.attname, c.collname
FROM pg_attribute a
JOIN pg_class t ON a.attrelid = t.oid
JOIN pg_collation c ON a.attcollation = c.oid
WHERE t.relname = 'your_table_name' AND a.attcollation <> 0;

2

Use the `ALTER TABLE ... ALTER COLUMN ... SET COLLATE` command to change the collation of the offending column(s). Replace `'your_table_name'`, `'your_column_name'`, and `'desired_collation'` with your specific values.

ALTER TABLE your_table_name
ALTER COLUMN your_column_name SET COLLATE 'desired_collation'; -- e.g., 'en_US.UTF-8' or 'C'

3

If the mismatch occurs across multiple tables or columns, you might need to repeat this for each instance. Be cautious as changing collation can affect existing data and index behavior.

ALTER TABLE another_table
ALTER COLUMN another_column SET COLLATE 'another_desired_collation';

3. Set Database-Level Default Collation medium

Change the default collation for all new objects created within a specific database.

1

Connect to the target PostgreSQL database using a superuser or a user with sufficient privileges.

psql -d your_database_name

2

Alter the database to set a new default collation. This will affect all new tables, columns, and other objects created in this database unless explicitly overridden.

ALTER DATABASE your_database_name SET default_collate = 'your_desired_collation'; -- e.g., 'en_US.UTF-8'

3

Verify the change by checking the database's settings.

SHOW default_collate;

4

Note: This change only affects newly created objects. Existing objects will retain their original collation. You may need to use Solution 2 for existing objects.

text

4. Ensure Consistent Client Encoding and Collation easy

Align client-side encoding and collation settings with the database to prevent issues during data transfer and operations.

1

When connecting to PostgreSQL, ensure that the client's encoding matches the database encoding. This is often set via the `PGCLIENTENCODING` environment variable or connection string parameter.

export PGCLIENTENCODING=UTF8

2

Some client applications or libraries allow specifying collation. If available, ensure this setting is consistent with the database's collation for text operations.

text

3

For `psql`, you can set the `CLIENT_ENCODING` parameter.

psql "dbname=your_database user=your_user host=your_host client_encoding='UTF8'"

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Related Errors

5 related errors

PostgreSQL Error 42P21: Collation Mismatch