MySQL 1205: Error in foreign key constraint.

Identify the Query and Table Causing the Error:

- To identify the problematic query and table, review your application's log files or enable MySQL's general log temporarily with:
SET global general_log = 1; SET global log_output = 'table';
After replicating the error, disable it with `SET global general_log = 0;` to avoid performance issues. Then, query the log:
SELECT argument FROM mysql.general_log WHERE argument LIKE '%FOREIGN KEY%';

Check for Inconsistencies in Schema Definitions:

- Ensure both tables involved in the foreign key constraint have the same column definitions (data type, length, etc.) for the foreign key and referenced key. Use the `DESCRIBE table_name;` command for both tables to compare.

Verify Data Types and Values:

- Ensure the foreign key column in the child table matches the corresponding primary key in the parent table in terms of data type and attributes. For instance, if one is `UNSIGNED` and the other is not, it could cause issues.

Check for Orphaned Rows:

- Check if there are any rows in the child table that do not have corresponding entries in the parent table. Run a query like:
SELECT * FROM childtable LEFT JOIN parenttable ON childtable.foreignkey = parenttable.primarykey WHERE parenttable.primarykey IS NULL;

Examine Locks:

- The error might be due to a lock. To check for locks, use:
SHOW ENGINE INNODB STATUS;
Look under the `LATEST FOREIGN KEY ERROR` section for details about the error and under `TRANSACTIONS` for any locked tables.

Correct or Remove the Erroneous Foreign Key Constraint:

- If a discrepancy is found or a decision is made to remove the constraint, first identify the constraint name with:
SELECT CONSTRAINTNAME FROM INFORMATIONSCHEMA.KEYCOLUMNUSAGE WHERE TABLENAME = 'yourtable_name';
- Then, drop the constraint (if decided):
ALTER TABLE yourtablename DROP FOREIGN KEY constraint_name;
- Or, correct the data causing the issue based on findings from steps 1-4.

If a Constraint Needs to Be Re-added or Created Anew:

- After correcting any issues, you can re-add or add a new constraint with:
ALTER TABLE childtable ADD CONSTRAINT fkname FOREIGN KEY (foreignkeycolumn) REFERENCES parenttable(parentkey_column);

Remember to replace `yourtablename`, `childtable`, `parenttable`, `foreignkeycolumn`, `parentkeycolumn`, and `fk_name` with your actual table and column names.

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MySQL Connection Issues

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MySQL Lock Contention

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MySQL Slow Queries

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MySQL 1252: Partition does not exist.

MySQL 1251: Key not allowed in partition.

MySQL 1250: Partition key not allowed.

MySQL 1247: Cannot split partition.

MySQL 1249: Cannot update partition index.

MySQL 1248: Cannot update partition schema.

MySQL 1246: Cannot merge partition.

MySQL 1244: Cannot create partition.

MySQL 1245: Cannot drop partition.

MySQL 1243: Statement failed due to partition.

MySQL 1242: Cannot expand partition.

MySQL 1240: Partition is corrupted.

MySQL 1241: Cannot shrink partition.

MySQL 1239: Partition needs repair.

MySQL 1236: Cannot access partition.

MySQL 1238: Cannot repair partition.

MySQL 1237: Partition is full.

MySQL 1234: Cannot unlock partition.

MySQL 1235: Statement not allowed in partition.

MySQL 1232: Cannot delete partition.

MySQL 1231: Cannot update partition.

MySQL 1233: Cannot lock partition.

MySQL 1230: Duplicate partition key.

MySQL 1229: Cannot drop partition.

MySQL 1228: Cannot add partition.

MySQL 1226: Failed to drop partition.

MySQL 1227: Failed to create partition.

MySQL 1222: Too many partitions.

MySQL 1212: Permission denied for key.

MySQL 1225: Duplicate partition name.

MySQL 1224: Partition not empty.

MySQL 1223: Partition key was not found.

MySQL 1221: Cannot delete parent row.

MySQL 1220: Cannot update parent row.

MySQL 1219: Cannot update child row.

MySQL 1216: Cannot delete or update a parent row.

MySQL 1218: Cannot delete child row.

MySQL 1215: Cannot add foreign key constraint.

MySQL 1217: Cannot add child row.

MySQL 1214: Row was updated.

MySQL 1213: Deadlock found when trying to get lock.

MySQL 1208: Failed to drop key.

MySQL 1211: Too many open files.

MySQL 1210: Key already exists.

MySQL 1209: Key not found.

MySQL 1204: Cannot update entry.

MySQL 1206: Error in unique key constraint.

MySQL 1207: Duplicate key found.

MySQL 1205: Error in foreign key constraint.

MySQL 1203: Cannot insert entry.

MySQL 1202: Cannot delete entry.

MySQL 1199: Statement failed due to index.

MySQL 1200: Index is corrupted.

MySQL 1201: Duplicate key value.

MySQL 1198: Error closing file.

MySQL 1193: Statement failed due to table.

MySQL 1197: Failed to open file.

MySQL 1175: Statement not allowed in schema.

MySQL 1196: Too many connections.

MySQL 1194: Table needs repair.

MySQL 1195: Table is corrupted.

MySQL 1192: Statement failed due to view.

MySQL 1191: Statement failed due to procedure.

MySQL 1189: Statement failed due to event.

MySQL 1190: Statement failed due to function.

MySQL 1186: SAVEPOINT cannot be rolled back.

MySQL 1188: Statement failed due to trigger.

MySQL 1187: Statement failed due to SAVEPOINT.

MySQL 1185: SAVEPOINT does not exist.

MySQL 1184: Cannot use SAVEPOINT in transaction.

MySQL 1183: Command not allowed in transaction.

MySQL 1182: Connection was closed.

MySQL 1181: Duplicate transaction.

MySQL 1180: Read-only transaction violation.

MySQL 1179: Transaction is read-only.

MySQL 1176: Statement not allowed in session.

MySQL 1178: Transaction not active.

MySQL 1177: Session not open.

MySQL 1174: Statement not allowed in row.

MySQL 1173: Statement not allowed in table.

MySQL 1172: Statement not allowed in transaction.

MySQL 1170: Cannot open database.

MySQL 1171: Null column in table.

MySQL 1169: Duplicate key.

MySQL 1168: Failed to create file.

MySQL 1167: Out of disk space.

MySQL 1165: Error reading from file.

MySQL 1166: Error writing to file.

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