Disable RETURNING clause for MySQL and MariaDB to fix SQL syntax errors #211

Copilot · 2025-12-16T04:32:16Z

MySQL 8.4.3 fails with syntax errors when attempting to use RETURNING clause in INSERT/UPDATE/DELETE statements. The code incorrectly assumed MySQL 8.0.21+ supported this PostgreSQL feature.

Changes

MySqlServerVersion.cs: Set Returning property to always return false (was >= 8.0.21)
MySqlUpdateSqlGenerator.cs: Updated comments to clarify RETURNING support status

Technical Details

MySQL: Does not support RETURNING in any version (tested 8.0.39, 8.4.3)

MariaDB: Partial support exists (INSERT/DELETE work since 10.0/10.5, UPDATE does not work). Disabled because EF Core's UpdateAndSelectSqlGenerator requires consistent support across all DML operations.

Both databases now use the fallback mechanism:

INSERT INTO `Drinks` (`Name`) VALUES (@p0);
SELECT `Id` FROM `Drinks`
WHERE ROW_COUNT() = 1 AND `Id` = LAST_INSERT_ID();

Impact

Fixes SQL syntax errors on MySQL 8.4.3+
No breaking changes - fallback mechanism already in use pre-8.0.21
MariaDB behavior unchanged (RETURNING was already disabled)

Original prompt

This section details on the original issue you should resolve

<issue_title>You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'RETURNING Id;</issue_title>
<issue_description>MySQL 8.4.3 failing with this error, ensure that any changes to fix this keeps working for MariaDB 11.6.2

Failed Pomelo.EntityFrameworkCore.MySql.FunctionalTests.Query.TPHInheritanceQueryMySqlTest.Can_filter_all_animals(async: False) [1 ms]
  Error Message:
   Microsoft.EntityFrameworkCore.DbUpdateException : An error occurred while saving the entity changes. See the inner exception for details.
---- MySqlConnector.MySqlException : You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'RETURNING `Id`;
INSERT INTO `Drinks` (`LiltCO2`, `Discriminator`, `SortIndex`, `' at line 3
  Stack Trace:
     at Microsoft.EntityFrameworkCore.Update.ReaderModificationCommandBatch.ExecuteAsync(IRelationalConnection connection, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.Update.Internal.BatchExecutor.ExecuteAsync(IEnumerable`1 commandBatches, IRelationalConnection connection, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.Update.Internal.BatchExecutor.ExecuteAsync(IEnumerable`1 commandBatches, IRelationalConnection connection, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.Update.Internal.BatchExecutor.ExecuteAsync(IEnumerable`1 commandBatches, IRelationalConnection connection, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.Storage.RelationalDatabase.SaveChangesAsync(IList`1 entries, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.SaveChangesAsync(IList`1 entriesToSave, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.SaveChangesAsync(StateManager stateManager, Boolean acceptAllChangesOnSuccess, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.Storage.ExecutionStrategy.<>c__DisplayClass30_0`2.<<ExecuteAsync>b__0>d.MoveNext()
--- End of stack trace from previous location ---
   at Microsoft.EntityFrameworkCore.Storage.ExecutionStrategy.ExecuteImplementationAsync[TState,TResult](Func`4 operation, Func`4 verifySucceeded, TState state, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.Storage.ExecutionStrategy.ExecuteImplementationAsync[TState,TResult](Func`4 operation, Func`4 verifySucceeded, TState state, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.Storage.ExecutionStrategy.ExecuteAsync[TState,TResult](TState state, Func`4 operation, Func`4 verifySucceeded, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.DbContext.SaveChangesAsync(Boolean acceptAllChangesOnSuccess, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.DbContext.SaveChangesAsync(Boolean acceptAllChangesOnSuccess, CancellationToken cancellationToken)
   at Pomelo.EntityFrameworkCore.MySql.FunctionalTests.TestUtilities.MySqlTestStore.InitializeAsync(Func`1 createContext, Func`2 seed, Func`2 clean) in /home/runner/work/Pomelo.EntityFrameworkCore.MySql/Pomelo.EntityFrameworkCore.MySql/test/EFCore.MySql.FunctionalTests/TestUtilities/MySqlTestStore.cs:line 152
   at Pomelo.EntityFrameworkCore.MySql.FunctionalTests.TestUtilities.MySqlTestStore.InitializeAsync(Func`1 createContext, Func`2 seed, Func`2 clean) in /home/runner/work/Pomelo.EntityFrameworkCore.MySql/Pomelo.EntityFrameworkCore.MySql/test/EFCore.MySql.FunctionalTests/TestUtilities/MySqlTestStore.cs:line 154
   at Microsoft.EntityFrameworkCore.TestUtilities.TestStore.<>c__DisplayClass13_0.<<InitializeAsync>b__0>d.MoveNext()
--- End of stack trace from previous location ---
   at Microsoft.EntityFrameworkCore.TestUtilities.TestStoreIndex.CreateSharedAsync(String name, Func`1 initializeDatabase)
   at Microsoft.EntityFrameworkCore.TestUtilities.TestStore.InitializeAsync(IServiceProvider serviceProvider, Func`1 createContext, Func`2 seed, Func`2 clean)
   at Microsoft.EntityFrameworkCore.TestUtilities.RelationalTestStore.InitializeAsync(IServiceProvider serviceProvider, Func`1 createContext, Func`2 seed, Func`2 clean)
   at Microsoft.EntityFrameworkCore.SharedStoreFixtureBase`1.InitializeAsync()
----- Inner Stack Trace -----
   at MySqlConnector.Core.ServerSession.ReceiveReplyAsync(IOBehavior ioBehavior, CancellationToken cancellationToken) in /_/src/MySqlConnector/Core/ServerSession.cs:line 1125
   at MySqlConnector.Core.ResultSet.ReadResultSetHeaderAsync(IOBehavior ioBehavior) in /_/src/MySqlConnector/Core/ResultSet.cs:line 37
   at MySqlConnector.MySqlDataReader.ActivateResultSet(CancellationToken cancellationToken) in /_/src/MySqlConnector/MySqlDataReader.cs:line 133
   at MySqlConnector.MySqlDataReader.InitAsync(...

</details>



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- Fixes microting/Pomelo.EntityFrameworkCore.MySql#210

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Co-authored-by: renemadsen <[email protected]>

… MariaDB Co-authored-by: renemadsen <[email protected]>

renemadsen · 2025-12-16T04:59:37Z

@copilot Now that this is working, search documentation for MySQL versions 9.x and MariaDB versions 11.x and 12.x

Copilot · 2025-12-16T05:03:47Z

@copilot Now that this is working, search documentation for MySQL versions 9.x and MariaDB versions 11.x and 12.x

Research completed on MySQL 9.x and MariaDB 11.x/12.x RETURNING support:

MySQL 9.x (9.0, 9.1, 9.2):

❌ No RETURNING support for INSERT/UPDATE/DELETE
Same as MySQL 8.x - MySQL has never implemented RETURNING

MariaDB 11.x (11.0-11.6):

✅ INSERT ... RETURNING: Supported (since 10.5.0)
✅ DELETE ... RETURNING: Supported (since 10.0)
❌ UPDATE ... RETURNING: NOT supported (confirmed by testing 11.6.2)

MariaDB 12.0:

✅ INSERT ... RETURNING: Supported
✅ DELETE ... RETURNING: Supported
❌ UPDATE ... RETURNING: Still NOT supported

Conclusion:
Our fix remains correct for all versions. The Returning property must stay false because:

MySQL never supports RETURNING (including 9.x)
MariaDB lacks UPDATE...RETURNING support (11.x and 12.x)
EF Core's UpdateAndSelectSqlGenerator requires consistent support across all DML operations

The fallback mechanism (LAST_INSERT_ID() + SELECT) works correctly for all versions.

renemadsen · 2025-12-16T05:13:02Z

@copilot With respect to the difference in MySQL and Mariadb, this is broken for MySQL v8.0.40, MariaDB 10.5.27, but it works in MariaDB 11.6.2:

Failed Pomelo.EntityFrameworkCore.MySql.FunctionalTests.BulkUpdates.NorthwindBulkUpdatesMySqlTest.Delete_with_LeftJoin(async: False) [161 ms]
Error Message:
MySqlConnector.MySqlException : You can't specify target table 'o' for update in FROM clause
Stack Trace:
at MySqlConnector.Core.ServerSession.ReceiveReplyAsync(IOBehavior ioBehavior, CancellationToken cancellationToken) in //src/MySqlConnector/Core/ServerSession.cs:line 1125
at MySqlConnector.Core.ResultSet.ReadResultSetHeaderAsync(IOBehavior ioBehavior) in //src/MySqlConnector/Core/ResultSet.cs:line 37
at MySqlConnector.MySqlDataReader.ActivateResultSet(CancellationToken cancellationToken) in /_/src/MySqlConnector/MySqlDataReader.cs:line 133
at MySqlConnector.MySqlDataReader.InitAsync(CommandListPosition commandListPosition, ICommandPayloadCreator payloadCreator, IDictionary2 cachedProcedures, IMySqlCommand command, CommandBehavior behavior, Activity activity, IOBehavior ioBehavior, CancellationToken cancellationToken) in /_/src/MySqlConnector/MySqlDataReader.cs:line 489 at MySqlConnector.Core.CommandExecutor.ExecuteReaderAsync(CommandListPosition commandListPosition, ICommandPayloadCreator payloadCreator, CommandBehavior behavior, Activity activity, IOBehavior ioBehavior, CancellationToken cancellationToken) in /_/src/MySqlConnector/Core/CommandExecutor.cs:line 58 at MySqlConnector.MySqlCommand.ExecuteNonQueryAsync(IOBehavior ioBehavior, CancellationToken cancellationToken) in /_/src/MySqlConnector/MySqlCommand.cs:line 304 at MySqlConnector.MySqlCommand.ExecuteNonQuery() in /_/src/MySqlConnector/MySqlCommand.cs:line 108 at Microsoft.EntityFrameworkCore.Storage.RelationalCommand.ExecuteNonQuery(RelationalCommandParameterObject parameterObject) at Microsoft.EntityFrameworkCore.Query.RelationalShapedQueryCompilingExpressionVisitor.<>c.<NonQueryResult>b__30_0(DbContext _, ValueTuple3 state)
at Microsoft.EntityFrameworkCore.Storage.ExecutionStrategy.Execute[TState,TResult](TState state, Func3 operation, Func3 verifySucceeded)
at Microsoft.EntityFrameworkCore.Query.RelationalShapedQueryCompilingExpressionVisitor.NonQueryResult(RelationalQueryContext relationalQueryContext, RelationalCommandResolver relationalCommandResolver, Type contextType, CommandSource commandSource, Boolean threadSafetyChecksEnabled)
at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.ExecuteCore[TResult](Expression query, Boolean async, CancellationToken cancellationToken)
at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.Execute[TResult](Expression query)
at Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryProvider.Execute[TResult](Expression expression)
at Microsoft.EntityFrameworkCore.EntityFrameworkQueryableExtensions.ExecuteDelete[TSource](IQueryable1 source) at Microsoft.EntityFrameworkCore.TestUtilities.BulkUpdatesAsserter.<>c__DisplayClass6_01.<b__0>d.MoveNext()
--- End of stack trace from previous location ---
at Microsoft.EntityFrameworkCore.TestUtilities.TestHelpers.<>c__DisplayClass41_01.<<ExecuteWithStrategyInTransactionAsync>b__0>d.MoveNext() --- End of stack trace from previous location --- at Microsoft.EntityFrameworkCore.ExecutionStrategyExtensions.<>c__71.<b__7_0>d.MoveNext()
--- End of stack trace from previous location ---
at Microsoft.EntityFrameworkCore.Storage.ExecutionStrategy.<>c__DisplayClass30_02.<<ExecuteAsync>b__0>d.MoveNext() --- End of stack trace from previous location --- at Microsoft.EntityFrameworkCore.Storage.ExecutionStrategy.ExecuteImplementationAsync[TState,TResult](Func4 operation, Func4 verifySucceeded, TState state, CancellationToken cancellationToken) at Microsoft.EntityFrameworkCore.Storage.ExecutionStrategy.ExecuteImplementationAsync[TState,TResult](Func4 operation, Func4 verifySucceeded, TState state, CancellationToken cancellationToken) at Microsoft.EntityFrameworkCore.Storage.ExecutionStrategy.ExecuteAsync[TState,TResult](TState state, Func4 operation, Func4 verifySucceeded, CancellationToken cancellationToken) at Microsoft.EntityFrameworkCore.TestUtilities.TestHelpers.ExecuteWithStrategyInTransactionAsync[TContext](Func1 createContext, Action2 useTransaction, Func2 testOperation, Func2 nestedTestOperation1, Func2 nestedTestOperation2, Func`2 nestedTestOperation3)
at Pomelo.EntityFrameworkCore.MySql.FunctionalTests.BulkUpdates.NorthwindBulkUpdatesMySqlTest.Delete_with_LeftJoin(Boolean async) in /home/runner/work/Pomelo.EntityFrameworkCore.MySql/Pomelo.EntityFrameworkCore.MySql/test/EFCore.MySql.FunctionalTests/BulkUpdates/NorthwindBulkUpdatesMySqlTest.cs:line 557
--- End of stack trace from previous location ---

Copilot · 2025-12-16T05:15:12Z

@copilot With respect to the difference in MySQL and Mariadb, this is broken for MySQL v8.0.40, MariaDB 10.5.27, but it works in MariaDB 11.6.2:

Failed Pomelo.EntityFrameworkCore.MySql.FunctionalTe...

This is a separate issue unrelated to the RETURNING clause fix. The error "You can't specify target table 'o' for update in FROM clause" is a known MySQL limitation when using DELETE with self-referencing subqueries.

This is a MySQL/MariaDB version difference in how they handle DELETE statements with JOINs:

MySQL 8.0.40 and MariaDB 10.5.27: Enforce the restriction (fails)
MariaDB 11.6.2: Allows it (works)

The RETURNING clause changes I made don't affect this behavior - they only change how generated values are retrieved after INSERT/UPDATE/DELETE operations. This appears to be a pre-existing compatibility issue with the bulk delete query generation that's exposed by the version differences.

This would require a separate investigation into how Delete_with_LeftJoin generates its SQL and whether it needs version-specific handling.

Initial plan

46c071e

Copilot AI assigned Copilot and renemadsen Dec 16, 2025

Copilot started work on behalf of renemadsen December 16, 2025 04:32 View session

Copilot AI and others added 2 commits December 16, 2025 04:40

Fix MySQL RETURNING clause syntax error - disable RETURNING for MySQL

3e6a6c0

Co-authored-by: renemadsen <[email protected]>

Update comments to accurately describe RETURNING support in MySQL and…

7da5030

… MariaDB Co-authored-by: renemadsen <[email protected]>

Copilot AI changed the title ~~[WIP] Fix SQL syntax error for MySQL compatibility~~ Disable RETURNING clause for MySQL and MariaDB to fix SQL syntax errors Dec 16, 2025

Copilot AI requested a review from renemadsen December 16, 2025 04:58

Copilot finished work on behalf of renemadsen December 16, 2025 04:58

Copilot started work on behalf of renemadsen December 16, 2025 05:00 View session

Copilot finished work on behalf of renemadsen December 16, 2025 05:05

Copilot started work on behalf of renemadsen December 16, 2025 05:13 View session

renemadsen marked this pull request as ready for review December 16, 2025 05:16

Copilot finished work on behalf of renemadsen December 16, 2025 05:16

renemadsen merged commit 3a12ab0 into master Dec 16, 2025
19 of 39 checks passed

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Disable RETURNING clause for MySQL and MariaDB to fix SQL syntax errors #211

Disable RETURNING clause for MySQL and MariaDB to fix SQL syntax errors #211

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Disable RETURNING clause for MySQL and MariaDB to fix SQL syntax errors #211

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