<p>MySQL raises error 1486 when a partitioning function contains a constant, random, or timezone-dependent expression that makes partitions non-deterministic.</p>
<p>MySQL Error 1486 ER_WRONG_EXPR_IN_PARTITION_FUNC_ERROR occurs when a partition key uses constant, random, or timezone-dependent expressions. Replace the forbidden expression with a deterministic column or function to resolve the issue.</p>
Constant, random or timezone-dependent expressions in
MySQL throws this error when the PARTITION BY clause references a non-deterministic expression such as NOW(), RAND(), or a constant value. Partition keys must produce repeatable results so the storage engine can determine exactly where each row belongs at all times.
The optimiser blocks statements that attempt to create, modify, or reorganise partitions with invalid expressions. Fixing the error is important because undeterministic keys break partition pruning and can corrupt data placement.
The primary trigger is using disallowed functions or constants inside the partitioning expression. Examples include RAND(), UUID(), CURRENT_TIMESTAMP, values depending on @@session.time_zone, and literal constants.
MySQL 5.7, 8.0, and later versions enforce the rule uniformly across CREATE TABLE, ALTER TABLE, and CREATE INDEX ... ALGORITHM=INPLACE operations.
Rewrite the PARTITION BY clause to reference only deterministic columns or deterministic built-in functions such as TO_DAYS(), YEAR(), or UNIX_TIMESTAMP(col). Update or recreate the table if needed.
After changing the partition key, reload or reorganise partitions to ensure proper data placement. Test on a staging database first to confirm performance.
Scenario: Partitioning by YEAR(NOW()). Solution: Store the date in a column created_at and partition by YEAR(created_at).
Scenario: Using RAND(id) in key. Solution: Remove RAND() and use HASH(id).
Design tables with deterministic partition keys from the outset. Avoid session-dependent functions, server variables, and constants. Document partitioning rules in Galaxy so team members reuse validated patterns.
Use Galaxy’s query endorsement to share correct CREATE TABLE templates, preventing accidental misuse of disallowed expressions.
Error 1503 ER_PARTITION_COLUMN_LIST_ERROR arises when a partition key column is missing from primary key; fix by including it in the key definition.
Error 1732 ER_SUBPARTITION_ERROR appears when subpartitioning options are invalid; verify HASH or KEY syntax.
Using NOW(), RAND(), UUID(), or SYSDATE() in the PARTITION BY clause triggers the error because results vary per row or per call.
Expressions that rely on @@session.time_zone or CONVERT_TZ() produce different outcomes across sessions, violating determinism.
Partitioning by a fixed constant such as 1 or 'US' provides no distribution logic and is therefore blocked.
Combining valid functions with a random element like UNIX_TIMESTAMP(col)+RAND() still invalidates the entire expression.
Occurs when partition columns are not part of every unique key. Add the partition column to all unique indexes.
Raised for invalid subpartition options such as mixing RANGE with HASH incorrectly.
Appears when ALTER TABLE changes partition counts inconsistently; ensure new partition count matches reorganisation rules.
No. It can appear during ALTER TABLE, EXCHANGE PARTITION, and any DDL that touches partition metadata.
No. The partitioning determinism rule is hard-coded and not affected by sql_mode toggles.
Yes. TO_DAYS(date_column) is deterministic and officially recommended by MySQL documentation.
Galaxy lets teams store approved CREATE TABLE templates. Its AI copilot flags non-deterministic functions, reducing the chance of pushing invalid DDL.
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