BadSqlGrammarException when attempting to use bound parameters in an `on conflict` clause

## Bug Report



#### Versions

- Driver: 1.0.9.RELEASE
- Database: 15.3.0
- Java: 
   openjdk 25.0.1 2025-10-21 LTS
   OpenJDK Runtime Environment Temurin-25.0.1+8 (build 25.0.1+8-LTS)
   OpenJDK 64-Bit Server VM Temurin-25.0.1+8 (build 25.0.1+8-LTS, mixed mode, sharing)
- OS: Sonoma 14.2.1 (23C71)

#### Current Behavior


I have a project in which there is a partial unique index. My team prefers specifying the predicate of the partial index with explicit parameters and binding them in the code, so that the usages of bound parameters are visible in the IDE. We've used this approach a lot in jdbc.

When trying to execute a query with such a partial index postgres states that "there is no unique or exclusion constraint matching the ON CONFLICT specification" and i get a BadSqlGrammarException. (Most of the times but sometimes it executes with no problem)

Tried it with both postgres enums and regular string values with explicit type casts as parameters in the predicate and it fails consistently. It only seems to work when writing the `on conflict` clause by hand

<details>
<summary>Stack trace</summary>

```
org.springframework.r2dbc.BadSqlGrammarException: execute; bad SQL grammar [
            INSERT INTO test(
                uq_column, status 
            ) VALUES (
                :uqColumn, :status
            )
            ON CONFLICT (uq_column) WHERE status IN (:prepared, :inProgress)
            DO NOTHING
            ]

	at org.springframework.r2dbc.connection.ConnectionFactoryUtils.convertR2dbcException(ConnectionFactoryUtils.java:255)
	at org.springframework.r2dbc.core.DefaultDatabaseClient.lambda$inConnection$4(DefaultDatabaseClient.java:135)
	at reactor.core.publisher.Mono.lambda$onErrorMap$27(Mono.java:3769)
	at reactor.core.publisher.Mono.lambda$onErrorResume$29(Mono.java:3859)
	at reactor.core.publisher.FluxOnErrorResume$ResumeSubscriber.onError(FluxOnErrorResume.java:94)
	at reactor.core.publisher.MonoUsingWhen$MonoUsingWhenSubscriber.deferredError(MonoUsingWhen.java:277)
	at reactor.core.publisher.FluxUsingWhen$RollbackInner.onComplete(FluxUsingWhen.java:475)
	at reactor.core.publisher.Operators$MultiSubscriptionSubscriber.onComplete(Operators.java:2205)
	at reactor.core.publisher.FluxPeek$PeekSubscriber.onComplete(FluxPeek.java:260)
	at reactor.core.publisher.Operators$MultiSubscriptionSubscriber.onComplete(Operators.java:2205)
	at reactor.core.publisher.MonoIgnoreThen$ThenIgnoreMain.onComplete(MonoIgnoreThen.java:209)
	at reactor.core.publisher.MonoIgnoreThen$ThenIgnoreMain.onComplete(MonoIgnoreThen.java:209)
	at reactor.pool.SimpleDequePool.maybeRecycleAndDrain(SimpleDequePool.java:540)
	at reactor.pool.SimpleDequePool$QueuePoolRecyclerInner.onComplete(SimpleDequePool.java:781)
	at reactor.core.publisher.Operators.complete(Operators.java:137)
	at reactor.core.publisher.MonoEmpty.subscribe(MonoEmpty.java:46)
	at reactor.core.publisher.Mono.subscribe(Mono.java:4496)
	at reactor.pool.SimpleDequePool$QueuePoolRecyclerMono.subscribe(SimpleDequePool.java:893)
	at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:53)
	at reactor.core.publisher.MonoIgnoreThen$ThenIgnoreMain.subscribeNext(MonoIgnoreThen.java:240)
	at reactor.core.publisher.MonoIgnoreThen$ThenIgnoreMain.onComplete(MonoIgnoreThen.java:203)
	at reactor.core.publisher.FluxPeek$PeekSubscriber.onComplete(FluxPeek.java:260)
	at reactor.core.publisher.Operators.complete(Operators.java:137)
	at reactor.core.publisher.MonoEmpty.subscribe(MonoEmpty.java:46)
	at reactor.core.publisher.Mono.subscribe(Mono.java:4496)
	at reactor.core.publisher.MonoIgnoreThen$ThenIgnoreMain.subscribeNext(MonoIgnoreThen.java:263)
	at reactor.core.publisher.MonoIgnoreThen.subscribe(MonoIgnoreThen.java:51)
	at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:53)
	at reactor.core.publisher.MonoIgnoreThen$ThenIgnoreMain.subscribeNext(MonoIgnoreThen.java:240)
	at reactor.core.publisher.MonoIgnoreThen$ThenIgnoreMain.onComplete(MonoIgnoreThen.java:203)
	at reactor.core.publisher.MonoIgnoreElements$IgnoreElementsSubscriber.onComplete(MonoIgnoreElements.java:89)
	at reactor.core.publisher.FluxHandleFuseable$HandleFuseableSubscriber.onComplete(FluxHandleFuseable.java:239)
	at reactor.core.publisher.MonoSupplier$MonoSupplierSubscription.request(MonoSupplier.java:148)
	at reactor.core.publisher.FluxHandleFuseable$HandleFuseableSubscriber.request(FluxHandleFuseable.java:260)
	at reactor.core.publisher.MonoIgnoreElements$IgnoreElementsSubscriber.onSubscribe(MonoIgnoreElements.java:72)
	at reactor.core.publisher.FluxHandleFuseable$HandleFuseableSubscriber.onSubscribe(FluxHandleFuseable.java:164)
	at reactor.core.publisher.MonoSupplier.subscribe(MonoSupplier.java:48)
	at reactor.core.publisher.Mono.subscribe(Mono.java:4496)
	at reactor.core.publisher.MonoIgnoreThen$ThenIgnoreMain.subscribeNext(MonoIgnoreThen.java:263)
	at reactor.core.publisher.MonoIgnoreThen.subscribe(MonoIgnoreThen.java:51)
	at reactor.core.publisher.InternalMonoOperator.subscribe(InternalMonoOperator.java:64)
	at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:53)
	at reactor.core.publisher.Mono.subscribe(Mono.java:4496)
	at reactor.core.publisher.FluxOnErrorResume$ResumeSubscriber.onError(FluxOnErrorResume.java:103)
	at reactor.core.publisher.MonoIgnoreElements$IgnoreElementsSubscriber.onError(MonoIgnoreElements.java:84)
	at reactor.core.publisher.FluxMap$MapSubscriber.onError(FluxMap.java:134)
	at reactor.core.publisher.FluxFilter$FilterSubscriber.onError(FluxFilter.java:157)
	at reactor.core.publisher.FluxFilter$FilterConditionalSubscriber.onError(FluxFilter.java:291)
	at reactor.core.publisher.FluxMap$MapConditionalSubscriber.onError(FluxMap.java:265)
	at reactor.core.publisher.Operators.error(Operators.java:198)
	at reactor.core.publisher.MonoError.subscribe(MonoError.java:53)
	at reactor.core.publisher.MonoDeferContextual.subscribe(MonoDeferContextual.java:55)
	at reactor.core.publisher.InternalMonoOperator.subscribe(InternalMonoOperator.java:64)
	at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:53)
	at reactor.core.publisher.Mono.subscribe(Mono.java:4496)
	at reactor.core.publisher.FluxUsingWhen$UsingWhenSubscriber.onError(FluxUsingWhen.java:364)
	at reactor.core.publisher.MonoStreamCollector$StreamCollectorSubscriber.onError(MonoStreamCollector.java:149)
	at reactor.core.publisher.FluxMap$MapSubscriber.onError(FluxMap.java:134)
	at reactor.core.publisher.FluxFlatMap$FlatMapMain.checkTerminated(FluxFlatMap.java:843)
	at reactor.core.publisher.FluxFlatMap$FlatMapMain.drainLoop(FluxFlatMap.java:609)
	at reactor.core.publisher.FluxFlatMap$FlatMapMain.drain(FluxFlatMap.java:589)
	at reactor.core.publisher.FluxFlatMap$FlatMapMain.innerError(FluxFlatMap.java:864)
	at reactor.core.publisher.FluxFlatMap$FlatMapInner.onError(FluxFlatMap.java:991)
	at reactor.core.publisher.FluxHandleFuseable$HandleFuseableSubscriber.onError(FluxHandleFuseable.java:229)
	at reactor.core.publisher.MonoCollectList$MonoCollectListSubscriber.onError(MonoCollectList.java:108)
	at reactor.core.publisher.FluxHandle$HandleSubscriber.onError(FluxHandle.java:213)
	at reactor.core.publisher.MonoFlatMapMany$FlatMapManyInner.onError(MonoFlatMapMany.java:255)
	at reactor.core.publisher.FluxHandleFuseable$HandleFuseableSubscriber.onNext(FluxHandleFuseable.java:201)
	at reactor.core.publisher.FluxFilterFuseable$FilterFuseableConditionalSubscriber.onNext(FluxFilterFuseable.java:337)
	at reactor.core.publisher.FluxContextWrite$ContextWriteSubscriber.onNext(FluxContextWrite.java:107)
	at reactor.core.publisher.FluxPeekFuseable$PeekConditionalSubscriber.onNext(FluxPeekFuseable.java:854)
	at reactor.core.publisher.FluxPeekFuseable$PeekConditionalSubscriber.onNext(FluxPeekFuseable.java:854)
	at io.r2dbc.postgresql.util.FluxDiscardOnCancel$FluxDiscardOnCancelSubscriber.onNext(FluxDiscardOnCancel.java:91)
	at reactor.core.publisher.FluxDoFinally$DoFinallySubscriber.onNext(FluxDoFinally.java:113)
	at reactor.core.publisher.FluxHandle$HandleSubscriber.onNext(FluxHandle.java:129)
	at reactor.core.publisher.FluxCreate$BufferAsyncSink.drain(FluxCreate.java:878)
	at reactor.core.publisher.FluxCreate$BufferAsyncSink.next(FluxCreate.java:803)
	at reactor.core.publisher.FluxCreate$SerializedFluxSink.next(FluxCreate.java:161)
	at io.r2dbc.postgresql.client.ReactorNettyClient$Conversation.emit(ReactorNettyClient.java:699)
	at io.r2dbc.postgresql.client.ReactorNettyClient$BackendMessageSubscriber.emit(ReactorNettyClient.java:951)
	at io.r2dbc.postgresql.client.ReactorNettyClient$BackendMessageSubscriber.onNext(ReactorNettyClient.java:825)
	at io.r2dbc.postgresql.client.ReactorNettyClient$BackendMessageSubscriber.onNext(ReactorNettyClient.java:731)
	at reactor.core.publisher.FluxHandle$HandleSubscriber.onNext(FluxHandle.java:129)
	at reactor.core.publisher.FluxPeekFuseable$PeekConditionalSubscriber.onNext(FluxPeekFuseable.java:854)
	at reactor.core.publisher.FluxMap$MapConditionalSubscriber.onNext(FluxMap.java:224)
	at reactor.core.publisher.FluxMap$MapConditionalSubscriber.onNext(FluxMap.java:224)
	at reactor.netty.channel.FluxReceive.drainReceiver(FluxReceive.java:294)
	at reactor.netty.channel.FluxReceive.onInboundNext(FluxReceive.java:403)
	at reactor.netty.channel.ChannelOperations.onInboundNext(ChannelOperations.java:425)
	at reactor.netty.channel.ChannelOperationsHandler.channelRead(ChannelOperationsHandler.java:115)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:444)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420)
	at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:412)
	at io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:346)
	at io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:333)
	at io.netty.handler.codec.ByteToMessageDecoder.callDecode(ByteToMessageDecoder.java:455)
	at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:290)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:444)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420)
	at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:412)
	at io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1407)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:440)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420)
	at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:918)
	at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:166)
	at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:788)
	at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:724)
	at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:650)
	at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:562)
	at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:994)
	at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74)
	at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
	at java.base/java.lang.Thread.run(Thread.java:1474)
	Suppressed: java.lang.Exception: #block terminated with an error
		at reactor.core.publisher.BlockingSingleSubscriber.blockingGet(BlockingSingleSubscriber.java:103)
		at reactor.core.publisher.Mono.block(Mono.java:1712)
		at Test.on conflict unsafe enum biding blocking(Test.kt:87)
Caused by: io.r2dbc.postgresql.ExceptionFactory$PostgresqlBadGrammarException: [42P10] there is no unique or exclusion constraint matching the ON CONFLICT specification
	at io.r2dbc.postgresql.ExceptionFactory.createException(ExceptionFactory.java:96)
	at io.r2dbc.postgresql.ExceptionFactory.createException(ExceptionFactory.java:65)
	at io.r2dbc.postgresql.ExceptionFactory.handleErrorResponse(ExceptionFactory.java:132)
	at reactor.core.publisher.FluxHandleFuseable$HandleFuseableSubscriber.onNext(FluxHandleFuseable.java:179)
	... 45 more
```

</details>
 
#### Table schema



<details>
<summary>Input Code</summary>

Here is the schema and an example query that i used to reproduce the problem
```sql
CREATE TYPE status_enum AS ENUM('PREPARED', 'IN_PROGRESS', 'FINISHED', 'CANCELLED');

CREATE TABLE test(
            id BIGSERIAL NOT NULL PRIMARY KEY,
            uq_column BIGINT NOT NULL,
            status status_enum NOT NULL
);

CREATE UNIQUE INDEX test_uq_column_uq_partial_idx ON test(uq_column) WHERE status IN ('PREPARED', 'IN_PROGRESS');
```

This code does not work:
```kotlin
databaseClient.sql(
            """
            INSERT INTO test(
                uq_column, status 
            ) VALUES (
                :uqColumn, :status
            )
            ON CONFLICT (uq_column) WHERE status IN (:prepared, :inProgress)
            DO NOTHING
            """
        )
            .bind("uqColumn", 101L)
            .bind("status", StatusEnum.PREPARED)
            .bind("prepared", StatusEnum.PREPARED)
            .bind("inProgress", StatusEnum.IN_PROGRESS)
            .fetch()
            .rowsUpdated()
            .block()
```

This code works:
```kotlin
databaseClient.sql(
            """
            INSERT INTO test(
                uq_column, status 
            ) VALUES (
                :uqColumn, :status
            )
            ON CONFLICT (uq_column) WHERE status IN ('PREPARED', 'IN_PROGRESS')
            DO NOTHING
            """
        )
            .bind("uqColumn", 101L)
            .bind("status", StatusEnum.PREPARED)
            // .bind("prepared", StatusEnum.PREPARED)
            // .bind("inProgress", StatusEnum.IN_PROGRESS)
            .fetch()
            .rowsUpdated()
            .block()
```
</details>

#### Steps to reproduce



<details>
<summary>Input Code</summary>

Here is the repo with junit tests to reproduce the problem. This is the closest match in terms of dependencies to the project that i initially encountered the problem in. There are suspend tests because at first i thought that the problem is related to kotlinx-coroutines-reactor usage which it seems not to be

https://github.com/s1mp3-a/r2dbc-postgres-on-conflict-issue

</details>

#### Expected behavior/code


I expect the query to execute successfully instead of triggering an sql exception

#### Additional context
The problem seems to be inconsistent such that some times little to no "unsafe" tests would pass and other times   around half of the repetitions would. I also tried bumping first the driver version to 1.1.1.RELEASE then the postgres version to 18.1 but still the problem persisted.

Looking at the postgres logs in failed tests i see that OID lookup for the enum type happens after the query error. However, that does not explain the case why binding strings with type casts fails

<details>
<summary>Logs</summary>

```
2026-01-26 20:16:58.218 MSK [63804] LOG:  statement: SHOW TRANSACTION ISOLATION LEVEL
2026-01-26 20:16:58.218 MSK [63802] ERROR:  there is no unique or exclusion constraint matching the ON CONFLICT specification
2026-01-26 20:16:58.218 MSK [63802] CONTEXT:  portal "B_10" with parameters: $1 = '101', $2 = 'PREPARED', $3 = 'PREPARED', $4 = 'IN_PROGRESS'
2026-01-26 20:16:58.218 MSK [63802] STATEMENT:  
	            INSERT INTO test(
	                uq_column, status 
	            ) VALUES (
	                $1, $2
	            )
	            ON CONFLICT (uq_column) WHERE status IN ($3, $4)
	            DO NOTHING
	            
2026-01-26 20:16:58.218 MSK [63804] LOG:  statement: SELECT pg_type.oid, pg_type.*   FROM pg_catalog.pg_type   LEFT   JOIN (select ns.oid as nspoid, ns.nspname, r.r           from pg_namespace as ns           join ( select s.r, (current_schemas(false))[s.r] as nspname                    from generate_series(1, array_upper(current_schemas(false), 1)) as s(r) ) as r          using ( nspname )        ) as sp     ON sp.nspoid = typnamespace  WHERE typname IN ('status_enum')  ORDER BY sp.r, pg_type.oid DESC ;
2026-01-26 20:16:58.223 MSK [63804] LOG:  statement: SELECT oid, * FROM pg_catalog.pg_type WHERE typname IN ('hstore','geometry','vector')
```

</details>

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BadSqlGrammarException when attempting to use bound parameters in an `on conflict` clause #700

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BadSqlGrammarException when attempting to use bound parameters in an on conflict clause #700

Description

Bug Report

Versions

Current Behavior

Table schema

Steps to reproduce

Expected behavior/code

Additional context

Metadata

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Issue actions

BadSqlGrammarException when attempting to use bound parameters in an `on conflict` clause #700