<p>MySQL raises error 1489 when you specify a list of partitioning columns in a HASH partition; lists are allowed only in KEY partitions.</p>
<p>MySQL Error 1489: ER_LIST_OF_FIELDS_ONLY_IN_HASH_ERROR appears when a HASH partition definition includes a list of columns. Use KEY partitioning or switch to a single-column HASH definition to resolve the issue.</p>
List of fields is only allowed in KEY partitions
The exact error message is: "List of fields is only allowed in KEY partitions." MySQL throws it during CREATE TABLE or ALTER TABLE when the partitioning clause violates engine rules.
The error means you tried to define a HASH partition on multiple columns. MySQL allows multi-column lists only in KEY partitioning, not HASH partitioning.
The primary trigger is including more than one column in a PARTITION BY HASH() expression. MySQL expects a single deterministic value, so a list breaks validation.
Using the PARTITION BY HASH COLUMNS syntax in older MySQL versions can also raise the error because only KEY partitioning supports the COLUMNS modifier.
The quickest fix is to switch from HASH to KEY partitioning when you need multiple columns. KEY distributes rows by a hash of all listed columns.
If HASH partitioning is mandatory, reduce the expression to one column or create a composite functional hash such as MD5() on concatenated values.
Creating a fact table with HASH partitioning on (user_id, event_date) triggers the error. Convert the statement to PARTITION BY KEY(user_id, event_date) to succeed.
Altering an existing table from KEY to HASH while retaining two columns will fail. Drop extra columns from the HASH expression or revert to KEY.
Choose partitioning strategy early in design. Use KEY for multi-column distribution and HASH for high-cardinality single columns.
Validate DDL in a staging environment or Galaxy’s AI copilot, which flags unsupported partition clauses before production deploys.
Error 1493 ER_PARTITION_FUNC_NOT_ALLOWED
Error 1503 ER_PARTITION_COLUMN_LIST_ERROR
Specifying PARTITION BY HASH(user_id, order_id) causes the error because HASH accepts one column only.
PARTITION BY HASH COLUMNS(user_id) syntax is legal only for KEY partitions in MySQL 5.7+.
Developers often reuse KEY partition samples but forget to change the partitioning type.
Raised when the number of partitioning columns does not match the primary key.
Occurs when a partitioning expression contains disallowed functions.
Indicates partition constant expressions evaluate outside permitted ranges.
No. HASH supports only single-column or expression-based keys. Use KEY partitioning for lists.
No. MySQL 8.0 retains the restriction: lists belong only in KEY partitions.
CRC32 or MD5 hashing adds CPU cost but often negligible compared to IO savings from balanced partitions.
Galaxy’s AI copilot parses DDL and warns when a HASH partition includes multiple columns, guiding you to the correct syntax.
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