Error
Error Code:
1808
MySQL Error 1808: Resolving Table Schema Mismatch
Description
Error 1808, "Schema mismatch," occurs when MySQL detects an inconsistency between the expected structure of a table and its actual definition. This typically arises during database operations that involve altering, moving, or referencing tables where their schema doesn't align with the current database context or internal data dictionary.
Error Message
Schema mismatch (%s)
Known Causes
4 known causesIncomplete Schema Alteration
This error can occur if an ALTER TABLE or RENAME TABLE operation was interrupted or did not complete successfully, leaving the table's metadata in an inconsistent state.
Manual Table File Movement
Directly moving or copying .frm files (table definition) without their corresponding data files (.ibd) or without updating the MySQL data dictionary can lead to schema inconsistencies.
Internal Data Dictionary Corruption
Rare corruption within MySQL's internal data dictionary can cause the server to misinterpret a table's schema, leading to this mismatch error.
Restoring Across MySQL Versions
Restoring a table from a backup created with a different major MySQL version can sometimes result in schema inconsistencies due to changes in internal table formats.
Solutions
3 solutions available1. Synchronize Table Definitions Between Instances medium
Ensure the schema of the affected table is identical on both the source and target MySQL instances.
1
Identify the table experiencing the schema mismatch. This is often indicated by the specific table name in the error message or the context of the operation (e.g., replication, federated tables).
2
On the source MySQL instance, retrieve the `CREATE TABLE` statement for the problematic table.
SHOW CREATE TABLE your_database_name.your_table_name;3
On the target MySQL instance, compare the `CREATE TABLE` statement with the one from the source. Look for differences in column definitions, indexes, constraints, table options (e.g., engine, charset), etc.
SHOW CREATE TABLE your_database_name.your_table_name;4
If differences are found, modify the table on the target instance to match the source. This might involve `ALTER TABLE` statements.
ALTER TABLE your_database_name.your_table_name MODIFY COLUMN your_column_name VARCHAR(255) NOT NULL DEFAULT '';
ALTER TABLE your_database_name.your_table_name ADD INDEX index_name (column1, column2);5
If significant differences exist or the table is new, consider dropping and recreating the table on the target instance using the `CREATE TABLE` statement from the source.
DROP TABLE IF EXISTS your_database_name.your_table_name;
-- Paste the SHOW CREATE TABLE output here, modified as needed6
After synchronization, retry the operation that caused the error.
2. Rebuild Federated Table easy
For federated tables, re-establishing the connection and schema definition can resolve mismatches.
1
Identify the federated table on your local MySQL instance that is causing the error.
2
Use the `SHOW CREATE TABLE` statement to view the definition of the federated table.
SHOW CREATE TABLE your_database_name.your_federated_table_name;3
Note the `CONNECTION` string and the `TABLE_NAME` specified in the `CREATE TABLE` statement.
4
Drop the federated table from your local MySQL instance.
DROP TABLE your_database_name.your_federated_table_name;5
Recreate the federated table using the exact `CREATE TABLE` statement obtained earlier. This forces MySQL to re-evaluate the schema of the remote table.
-- Paste the SHOW CREATE TABLE output from step 2, ensuring the CONNECTION and TABLE_NAME are correct.6
Attempt the operation that previously failed.
3. Verify Replication Slave Status and Schema medium
If the error occurs during replication, check the slave's status and ensure its schema is in sync with the master.
1
On the replication slave, check the status of the replication threads.
SHOW SLAVE STATUS\G;2
Look for errors in `Last_SQL_Errno` and `Last_SQL_Error`. If there's an error related to schema mismatch, note the error message.
3
If the error message indicates a schema mismatch, stop the replication slave.
STOP SLAVE;4
On the master server, retrieve the `CREATE TABLE` statement for the table involved in the replication error.
SHOW CREATE TABLE your_database_name.your_table_name;5
On the slave server, compare the schema of the table with the master's definition. Use `SHOW CREATE TABLE` on the slave.
SHOW CREATE TABLE your_database_name.your_table_name;6
Alter the table on the slave to match the master's schema. If the table is significantly out of sync or problematic, consider dropping and recreating it on the slave using the master's `CREATE TABLE` statement.
-- Example ALTER TABLE statement
ALTER TABLE your_database_name.your_table_name MODIFY COLUMN column_name VARCHAR(100) NOT NULL DEFAULT '';
-- Or for recreation:
DROP TABLE IF EXISTS your_database_name.your_table_name;
-- Paste master's SHOW CREATE TABLE output here7
Reset the slave's position to ensure it processes events correctly from the point of resolution.
SET GLOBAL SQL_SLAVE_SKIP_COUNTER = 1; -- Or use the appropriate number of events to skip if known.
START SLAVE;8
Monitor `SHOW SLAVE STATUS\G;` to ensure replication is running without errors.