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Description

This error occurs when a SQL operation attempts to combine or compare string data types that have conflicting or incompatible character sets and collations. MariaDB cannot implicitly resolve how to perform the operation, such as a JOIN, WHERE clause comparison, or UNION, between the different collation settings.

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Error Message

Illegal mix of collations (%s,%s) and (%s,%s) for operation '%s'

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Known Causes

4 known causes

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Incompatible Column Comparison

Occurs when comparing two columns (e.g., in a WHERE clause or JOIN condition) that are defined with different character sets and collations, and MariaDB cannot implicitly convert them.

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Literal String Collation Mismatch

This happens when a literal string (e.g., 'mystring') is compared or combined with a column that has a different collation, and the literal's default collation (often connection-level) conflicts.

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Cross-Object Collation Discrepancy

Operations involving tables or databases with differing default character sets and collations can lead to this error, especially in complex queries spanning multiple objects.

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Automatic Collation Coercion Failure

MariaDB's automatic rules for determining the resulting collation of an expression fail because the involved collations are too disparate or ambiguous for implicit resolution.

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Solutions

4 solutions available

1. Explicitly Specify Collation in Query easy

Temporarily resolve the issue by forcing a consistent collation within the problematic query.

1

Identify the query that is causing the error. This is usually indicated in the error message itself or in your application's logs.

2

Locate the columns involved in the comparison or operation that triggers the error. You can find this information in the error message (e.g., %s,%s).

3

Modify the query to explicitly cast one or both of the columns to a common, compatible collation. Choose a collation that is appropriate for your data.

SELECT * FROM table1 JOIN table2 ON CAST(table1.column1 AS CHAR CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci) = table2.column2;

4

Alternatively, you can use the `COLLATE` clause directly if the operation supports it.

SELECT * FROM table1 WHERE column1 COLLATE utf8mb4_unicode_ci = column2;

2. Alter Table to Standardize Collation medium

Permanently resolve the issue by changing the collation of one or more columns to match.

1

Determine the desired collation for your table(s). This should be a collation that supports all characters needed for your data and is consistent with your application's requirements.

2

Identify the tables and columns involved in the error. The error message often provides clues.

3

Use the `ALTER TABLE` statement to change the collation of the affected columns. It's recommended to back up your data before making schema changes.

ALTER TABLE your_table_name MODIFY COLUMN your_column_name VARCHAR(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;

4

Repeat the `ALTER TABLE` statement for all columns that need to have their collation standardized.

ALTER TABLE another_table MODIFY COLUMN another_column VARCHAR(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;

3. Set Default Collation for Database or Table medium

Prevent future occurrences by setting a consistent default collation at the database or table level.

1

Decide on a default collation that will be applied to all new tables and columns created within a specific database or for a specific table.

2

To set the default collation for an entire database (this will affect future table creations):

ALTER DATABASE your_database_name CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;

3

To set the default collation for a specific table (this will affect future column creations within this table):

ALTER TABLE your_table_name CONVERT TO CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;

4

Note: This solution primarily affects new objects. Existing columns with incompatible collations will still need to be altered as described in Solution 2.

4. Review Application Logic and Data Types advanced

Address the root cause by ensuring application code and data types align with intended collations.

1

Examine your application's code that interacts with the database. Look for instances where string data is being manipulated or compared without explicit collation handling.

2

Verify that the data types of columns involved in comparisons are consistent and appropriate for the intended collation (e.g., using `VARCHAR` or `TEXT` with the correct character set).

3

If your application dynamically constructs queries, ensure that it is aware of and handles potential collation mismatches. This might involve fetching column collation information from the database or enforcing a standard collation in your ORM.

4

Consider using a consistent character set and collation across your entire application and database to minimize such issues.

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Related Errors

5 related errors

MariaDB Error 1267: Incompatible Collation Mix