<p>MySQL raises this error when a function used in a partition key returns a data type that partitioning does not support.</p>
<p>MySQL Error 1491: ER_PARTITION_FUNC_NOT_ALLOWED_ERROR appears when the partitioning expression calls a function whose return type is disallowed in partitions. Replace the function or cast its result to an integer-compatible type to resolve the error.</p>
The %s function returns the wrong type
Error 1491 signals that the function named in the message is invalid in a partitioning expression because it returns a data type MySQL cannot hash or range-evaluate.
The error stops CREATE TABLE or ALTER TABLE operations that attempt to introduce such a partition definition, protecting table integrity.
The error arises during CREATE TABLE, ALTER TABLE, or EXCHANGE PARTITION statements when the partition key or subpartition key uses disallowed functions such as CONCAT, YEARWEEK, or non-deterministic expressions.
It also appears during replication if a partitioned table on the replica includes an invalid function that did not exist on the source.
Functions that return DECIMAL, FLOAT, DOUBLE, JSON, or spatial types cannot participate in partitioning expressions.
Expressions using NOW(), RAND(), UUID(), or other values that change per row or per call are forbidden in partition keys.
YEARWEEK(), WEEK(), or DATE_FORMAT() may yield string output, which violates partitioning requirements.
String functions that alter collation or length can trigger the error if their result is not a simple VARCHAR/BINARY with a permitted collation.
Similar message but triggered by non-deterministic or disallowed functions without type emphasis.
Occurs when partition function is not dependent on table columns, yielding a constant.
Raised when a partition function is not a constant expression for subpartitioning.
Yes, as long as the output is an integer or string type MySQL permits and the function is deterministic, for example, TO_DAYS(date_col).
It blocks only the statement that introduces an invalid partition expression. Existing data remains untouched.
MySQL 5.1 and later enforce strict rules on partitioning functions. Newer versions add more deterministic checks.
Galaxy highlights invalid partition functions in its SQL editor using lint rules and offers AI suggestions to rewrite the expression before execution.
.avif)
.avif){kind=logo}
