flink-cdc-connect/flink-cdc-source-connectors/flink-connector-db2-cdc/src/main/java/org/apache/flink/cdc/connectors/db2/source/utils/Db2Utils.java [122:150]:
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    public static Column getSplitColumn(Table table, @Nullable String chunkKeyColumn) {
        List<Column> primaryKeys = table.primaryKeyColumns();
        if (primaryKeys.isEmpty()) {
            throw new ValidationException(
                    String.format(
                            "Incremental snapshot for tables requires primary key,"
                                    + " but table %s doesn't have primary key.",
                            table.id()));
        }

        if (chunkKeyColumn != null) {
            Optional<Column> targetPkColumn =
                    primaryKeys.stream()
                            .filter(col -> chunkKeyColumn.equals(col.name()))
                            .findFirst();
            if (targetPkColumn.isPresent()) {
                return targetPkColumn.get();
            }
            throw new ValidationException(
                    String.format(
                            "Chunk key column '%s' doesn't exist in the primary key [%s] of the table %s.",
                            chunkKeyColumn,
                            primaryKeys.stream().map(Column::name).collect(Collectors.joining(",")),
                            table.id()));
        }

        // use first field in primary key as the split key
        return primaryKeys.get(0);
    }
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flink-cdc-connect/flink-cdc-source-connectors/flink-connector-sqlserver-cdc/src/main/java/org/apache/flink/cdc/connectors/sqlserver/source/utils/SqlServerUtils.java [126:154]:
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    public static Column getSplitColumn(Table table, @Nullable String chunkKeyColumn) {
        List<Column> primaryKeys = table.primaryKeyColumns();
        if (primaryKeys.isEmpty()) {
            throw new ValidationException(
                    String.format(
                            "Incremental snapshot for tables requires primary key,"
                                    + " but table %s doesn't have primary key.",
                            table.id()));
        }

        if (chunkKeyColumn != null) {
            Optional<Column> targetPkColumn =
                    primaryKeys.stream()
                            .filter(col -> chunkKeyColumn.equals(col.name()))
                            .findFirst();
            if (targetPkColumn.isPresent()) {
                return targetPkColumn.get();
            }
            throw new ValidationException(
                    String.format(
                            "Chunk key column '%s' doesn't exist in the primary key [%s] of the table %s.",
                            chunkKeyColumn,
                            primaryKeys.stream().map(Column::name).collect(Collectors.joining(",")),
                            table.id()));
        }

        // use first field in primary key as the split key
        return primaryKeys.get(0);
    }
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