<p>MySQL throws error 1502 when a column with BLOB or TEXT type is referenced in a partition function, key, or subpartitioning clause.</p>
<p>MySQL Error 1502: ER_BLOB_FIELD_IN_PART_FUNC_ERROR means a BLOB or TEXT column is used in a partition key or function, which MySQL forbids because large variable length fields break partition pruning. Cast or convert the column or remove it from the partition definition to resolve the issue.</p>
A BLOB field is not allowed in partition function
Error 1502 fires when a CREATE TABLE or ALTER TABLE statement tries to partition a table on a column declared as BLOB or TEXT. MySQL partitioning only supports deterministic, fixed length expressions in partition keys. Variable length LOB columns violate this rule, so the server rejects the statement.
The error text is often: "A BLOB field is not allowed in partition function". It stops execution before any partition metadata is written, protecting storage engines from unsupported layouts.
Developers see it while migrating large legacy tables to partitioning, especially when attempting RANGE or HASH partitioning on JSON, LONGTEXT, or MediumBLOB columns. It also occurs during table rebuilds triggered by ALTER TABLE ... MODIFY PARTITION and while adding subpartitions in versions prior to 8.0.31.
Leaving the table unpartitioned can lead to performance bottlenecks, long maintenance windows, and heavy lock contention. Correcting the schema enables efficient partition pruning, faster queries on time series data, and manageable backup rotations.
Partitioning columns must be integer, date, or fixed-length string types. BLOB and TEXT columns break the rule, leading directly to error 1502.
Composite partition keys that include a LOB column fail even if another column meets requirements. All columns in the key must be supported types.
Using functions like SUBSTRING on a TEXT column inside PARTITION BY HASH results in the same restriction because the underlying data type is variable length.
Triggers when non-deterministic functions like NOW() appear in partition expressions.
Raised when partition functions depend on mutable routine variables.
Occurs if the total length of partitioning columns exceeds the engine limit.
Yes, if the column length is <= 3072 bytes for InnoDB and you use RANGE or LIST partitioning with COLUMNS syntax.
No. Even in MySQL 8.0.34 BLOB and TEXT columns are still forbidden in partition keys.
No. CAST only changes how the value is returned, not the underlying data type stored in metadata, so the restriction remains.
Galaxy's AI copilot flags unsupported partition definitions in real time and suggests generated column strategies, preventing error 1502 before execution.
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