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Description

This error occurs when attempting to create a functional index (also known as an expression-based index) whose definition refers to a row value. Functional index expressions are designed to operate solely on the column(s) being indexed, or constants, and cannot access other data within the same row.

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Error Message

Expression of functional index '%s' cannot refer to a row value.

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Known Causes

3 known causes

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Invalid Expression Syntax

The functional index expression includes syntax that attempts to reference other columns from the same row or row-level attributes.

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Referencing Row-Specific Functions

Using functions or keywords within the index expression that are designed to access or operate on the entire row context, which is not allowed for functional indexes.

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Misunderstanding Index Scope

A conceptual misunderstanding of functional indexes, expecting them to behave like generated columns or triggers that can access other column values from the same row.

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Solutions

3 solutions available

1. Remove Row Value References from Functional Index Expression easy

Modify the functional index definition to exclude direct references to row values.

1

Identify the functional index causing the error. The error message will typically include the name of the index (e.g., `'%s'`).

SHOW CREATE TABLE your_table_name;

2

Examine the `CREATE INDEX` statement for that functional index. Look for expressions that directly reference a column name within the index definition itself, especially if it's intended to be part of the index key but is being treated as a row value.

CREATE INDEX index_name ON your_table_name ((column_a + column_b)); -- Example of potentially problematic syntax if 'column_a' or 'column_b' are intended to be fixed values

3

Remove or rephrase the expression to not refer to a row value. Functional indexes in MySQL are designed to index expressions that evaluate to a constant or a value derived from multiple columns in a deterministic way, not to index the row itself in a way that implies a self-reference.

DROP INDEX index_name ON your_table_name;
CREATE INDEX index_name ON your_table_name ((some_expression_without_direct_row_references));

4

If the intention was to index a computed value based on other columns, ensure the expression is valid for a functional index. For example, indexing the result of a function or a simple arithmetic operation between columns.

CREATE INDEX idx_full_name ON users ((CONCAT(first_name, ' ', last_name)));

2. Re-evaluate Indexing Strategy medium

Consider alternative indexing methods if the functional index is not suitable for the desired query pattern.

1

Analyze the queries that are failing or that you intended to optimize with the functional index. Understand what data the index was supposed to help retrieve.

EXPLAIN your_problematic_query;

2

If the functional index was meant to index a specific value that changes per row in a way that's not a deterministic expression, consider if a standard multi-column index or a generated column with an index would be more appropriate.

ALTER TABLE your_table_name
ADD COLUMN generated_column VARCHAR(255) AS (expression_that_evaluates_to_desired_value) STORED;
CREATE INDEX idx_generated_column ON your_table_name (generated_column);

3

Alternatively, if the expression involves a function that's not deterministic across rows (e.g., `RAND()`), it cannot be used in a functional index. In such cases, you might need to rely on other indexing strategies or reconsider the query logic.

SELECT * FROM your_table_name WHERE some_column = 'static_value'; -- If the query can be rewritten to avoid non-deterministic functions.

3. Update MySQL Server Version advanced

Ensure you are using a MySQL version that supports the intended functional index syntax and features.

1

Check your current MySQL server version.

SELECT VERSION();

2

Consult the MySQL documentation for your specific version to understand the limitations and correct syntax for functional indexes. Functional indexes were introduced in MySQL 8.0.

https://dev.mysql.com/doc/refman/8.0/en/create-index.html

3

If you are using an older version of MySQL, consider upgrading to MySQL 8.0 or later to leverage the full capabilities of functional indexes. This might involve planning a database upgrade process.

This step is a server administration task and will vary based on your OS and MySQL installation method. Consult your MySQL administrator or official MySQL upgrade guides.

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Related Errors

5 related errors

MySQL Error 3800: Functional Index Row Value Reference