client-v1 (clickhouse-data): "Duplicate key" IllegalStateException on result sets with duplicate column names (0.9.8)

スタックトレースで報告されているコンストラクターの位置にある ClickHouseDataProcessor$DefaultSerDe から開始し、提供された重複カラムのクエリを使って RowBinaryWithNamesAndTypes で再現します。カラム名からインデックスへのマップが重複した名前をどのように処理するかを確認し、位置ベースの読み取りが正常に完了することを検証します。重複した出力名によってレスポンスの構築や位置ベースのアクセスが妨げられなくなれば完了です。

Description

The v1 client (clickhouse-client / clickhouse-http-client 0.9.8) throws java.lang.IllegalStateException: Duplicate key ... when a query returns a result set with duplicate column names (which is valid SQL).

com.clickhouse.data.ClickHouseDataProcessor$DefaultSerDe builds a column-name → index map with Collectors.toMap (no merge function) at construction time, so any repeated column name fails immediately — before the caller can read anything, even when reading purely by position.

This reproduces with RowBinaryWithNamesAndTypes (the format that carries column names). A trivial SELECT key1, key1 FROM (SELECT 1 AS key1) is enough. Real-world trigger: a reporting tool that lets a user select the same projection twice (e.g. two Date columns), producing SQL like SELECT toDate(...) AS Date, toDate(...) AS Date, ....

This looks related to #2336 (reported on 0.8.4, marked fixed in 0.9.3 via #2618), but that fix was in the JDBC TableSchema (Guava ImmutableMap, "Multiple entries with same key"). The failure here is a different code path — ClickHouseDataProcessor using the JDK Collectors.toMap ("attempted merging values") — and still fails in 0.9.8.

Steps to reproduce

1. Use com.clickhouse:clickhouse-http-client:0.9.8 (v1 client).
2. Execute a query whose result has two columns with the same name, e.g. SELECT key1, key1 FROM (SELECT 1 AS key1), with format RowBinaryWithNamesAndTypes.
3. executeAndWait() / iterating response.records() throws.

Error Log or Exception StackTrace

java.lang.IllegalStateException: Duplicate key key1 (attempted merging values 0 and 1)
    at java.base/java.util.stream.Collectors.duplicateKeyException(Collectors.java:135)
    at java.base/java.util.stream.Collectors.lambda$uniqKeysMapAccumulator$0(Collectors.java:182)
    at java.base/java.util.stream.ReduceOps$3ReducingSink.accept(ReduceOps.java:169)
    at java.base/java.util.stream.IntPipeline$1$1.accept(IntPipeline.java:180)
    at java.base/java.util.stream.Streams$RangeIntSpliterator.forEachRemaining(Streams.java:104)
    at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:570)
    at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:560)
    at java.base/java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:921)
    at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:265)
    at java.base/java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:727)
    at com.clickhouse.data.ClickHouseDataProcessor$DefaultSerDe.<init>(ClickHouseDataProcessor.java:72)
    at com.clickhouse.client.http.ApacheHttpConnectionImpl ...
    at com.clickhouse.client.ClickHouseClient.executeAndWait(ClickHouseClient.java:894)

Expected Behaviour

Duplicate column names are valid in ClickHouse/SQL, so building the response must not throw. Reading values by position should always work; name-based lookup of a duplicated name can reasonably return the first match (or be documented). Suggestion: build the name→index map with a merge function (keep the first index) instead of the throwing Collectors.toMap.

Code Example

import com.clickhouse.client.*;
import com.clickhouse.data.ClickHouseFormat;
import com.clickhouse.data.ClickHouseRecord;

public class DuplicateColumnRepro {
  public static void main(String[] args) throws Exception {
    ClickHouseNode server = ClickHouseNode.builder()
        .host("localhost")
        .port(ClickHouseProtocol.HTTP, 8123)
        .build();

    try (ClickHouseClient client = ClickHouseClient.newInstance(server.getProtocol());
         ClickHouseResponse response = client.read(server)
             .format(ClickHouseFormat.RowBinaryWithNamesAndTypes)
             .query("SELECT key1, key1 FROM (SELECT 1 AS key1)") // duplicate output column name
             .executeAndWait()) {
      for (ClickHouseRecord r : response.records()) {
        System.out.println(r.getValue(0).asString() + ", " + r.getValue(1).asString());
      }
    }
    // throws: java.lang.IllegalStateException: Duplicate key key1 (attempted merging values 0 and 1)
  }
}

v2 — works (returns 1, 1):

Configuration

Client Configuration

client.read(server)
      .format(ClickHouseFormat.RowBinaryWithNamesAndTypes)
// Reproduces with the default provider; also confirmed with both
// HttpConnectionProvider.APACHE_HTTP_CLIENT and HttpConnectionProvider.HTTP_URL_CONNECTION.

Environment

• Cloud
• Client version: 0.9.8 (clickhouse-http-client / clickhouse-client / clickhouse-data)
• Language version: Java 24.0.2 (also reproduces on Java 17)
• OS: macOS (Darwin arm64); also Linux

ClickHouse Server

• ClickHouse Server version: 26.3.10.60
• ClickHouse Server non-default settings, if any: none relevant
• CREATE TABLE statements for tables involved: none needed — SELECT key1, key1 FROM (SELECT 1 AS key1) reproduces it without any table
• Sample data for all these tables: n/a