Description:
ALTER TABLE ... EXCHANGE PARTITION does not validate that check constraints match between the partitioned table and the swap table. This allows data that violates the swap table's check constraints to be silently moved into it.
The exchange succeeds unconditionally. The swap table ends up with rows that violate its own check constraints. Constraints ARE still enforced for new DML on the swap table, creating an inconsistency between existing and newly inserted rows.
Impact:
- Data integrity bypass: rows violating CHECK constraints can exist in the table after EXCHANGE PARTITION
- Constraints still enforced for new DML, creating inconsistency between existing and new rows
- No crash, but violates the contract that CHECK constraints guarantee about table data
Root Cause:
sql/sql_partition_admin.cc — check_exchange_partition() validates engine, temp table status, FK constraints, and partitioning, but has zero CHECK constraint validation. sql/sql_table.cc — mysql_compare_tables() compares column types, keys, and NULL behavior, but does not compare check constraints either.
Related:
- MariaDB MDEV-33127 — same issue, open/unresolved
- TiDB #45922 — same issue, fixed via PR #46021
- No existing MySQL bug as of 2026-04-01
Thank you,
Yakir Gibraltar
How to repeat:
CREATE TABLE t_part (
a INT,
CHECK (a > 0)
) PARTITION BY RANGE (a) (
PARTITION p0 VALUES LESS THAN (100),
PARTITION p1 VALUES LESS THAN MAXVALUE
);
CREATE TABLE t_swap (
a INT,
CHECK (a > 50)
);
INSERT INTO t_part PARTITION (p0) VALUES (10), (20);
-- Succeeds — no check constraint validation
ALTER TABLE t_part EXCHANGE PARTITION p0 WITH TABLE t_swap;
-- t_swap now contains rows violating its own CHECK (a > 50)
SELECT * FROM t_swap;
-- Returns: 10, 20
-- Constraint IS enforced for new inserts
INSERT INTO t_swap VALUES (5);
-- ERROR 3819 (HY000): Check constraint 't_swap_chk_1' is violated.
Expected: ALTER TABLE ... EXCHANGE PARTITION should reject the exchange when the partitioned table's data would violate the swap table's check constraints (or vice versa), unless WITHOUT VALIDATION is specified.
Actual: The exchange succeeds. t_swap ends up with rows (10, 20) that violate CHECK (a > 50), while new inserts are still blocked by the constraint.
Suggested fix:
In check_exchange_partition() (sql/sql_partition_admin.cc, lines 127-172) or in mysql_compare_tables() (sql/sql_table.cc, lines 13611-13682), add validation that iterates over check constraints on both tables and rejects the exchange if the swap table has constraints that the data from the partitioned table would violate.
Alternatively, extend the existing WITH VALIDATION row scan (sql/sql_partition_admin.cc) to also evaluate the swap table's CHECK constraints against each row being moved, similar to how DML enforces them.
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