Function buildJoinQuery

src/optimizer/foreign_join_push_down_optimizer.cpp:354–467

Build the SQL join query string and collect column names for result mapping. Keep result column names SQL-safe while using display names that preserve the user's labels.

// Build the SQL join query string and collect column names for result mapping.
// Keep result column names SQL-safe while using display names that preserve the user's labels.
static JoinQueryInfo buildJoinQuery(const ForeignJoinPatternInfo& info,
    const expression_vector& outputColumns, main::ClientContext* context) {
    auto extend = info.extend;
    auto srcNode = extend->getBoundNode();
    auto dstNode = extend->getNbrNode();
    auto rel = extend->getRel();

    // Get raw variable names (user-facing, like 'a', 'b', 'c')
    std::string srcAlias = srcNode->getVariableName();
    std::string dstAlias = dstNode->getVariableName();
    std::string relAlias = rel->getVariableName();

    // Determine join columns based on direction and foreign table schema
    std::string srcJoinCol, dstJoinCol;
    auto tableColumnNames =
        getForeignTableColumnNames(info.dbName, getUnqualifiedTableName(info.relTable), context);
    if (tableColumnNames.size() < 2) {
        throw RuntimeException(std::format(
            "Foreign join push down optimizer: unable to retrieve column names for table '{}.{}', "
            "got {} columns but need at least 2 for join",
            info.dbName, info.relTable, tableColumnNames.size()));
    }

    std::string firstCol = tableColumnNames[0];
    std::string secondCol = tableColumnNames[1];
    if (extend->getDirection() == ExtendDirection::FWD) {
        srcJoinCol = firstCol;
        dstJoinCol = secondCol;
    } else {
        srcJoinCol = secondCol;
        dstJoinCol = firstCol;
    }

    auto getNodeIDColumn = [&](const std::string& tableName) {
        auto columnNames =
            getForeignTableColumnNames(info.dbName, getUnqualifiedTableName(tableName), context);
        if (columnNames.empty()) {
            return std::string{InternalKeyword::ID};
        }
        return columnNames[0];
    };
    auto srcIDCol = getNodeIDColumn(info.srcTable);
    auto dstIDCol = getNodeIDColumn(info.dstTable);

    // Build SELECT items from output columns and collect column names
    std::vector<std::string> columnNames;
    std::vector<std::string> displayNames;

    for (auto& col : outputColumns) {
        std::string colExpr;
        std::string colName;
        std::string displayName;

        // Determine which table the column comes from based on variable name
        if (col->expressionType == ExpressionType::PROPERTY) {
            auto& prop = col->constCast<PropertyExpression>();
            // Use raw variable name for SQL query (e.g., 'a' instead of '_0_a')
            auto rawVarName = prop.getRawVariableName();