如何创建SELECT 1对应的RelNode？BigQuery场景下RelBuilder选哪个API？

Hey there! Let's tackle your two Calcite + BigQuery questions step by step:

1. Building the RelNode Equivalent to SELECT 1 #

To create a RelNode that represents the simple query SELECT 1, you'll use Calcite's RelBuilder to construct a single row with a literal value of 1. Here's a practical code example:

// Initialize RelBuilder with your BigQuery-configured environment
RelBuilder relBuilder = RelBuilder.create(bigQueryRelConfig);

// Build the RelNode for SELECT 1
RelNode selectOneRelNode = relBuilder
    // Optional: Define a column name (Calcite uses EXPR$0 by default if omitted)
    .values(Collections.singletonList("EXPR$0"), 
            // Pass a single row containing the literal 1
            Collections.singletonList(Collections.singletonList(relBuilder.literal(1))))
    .build();

This generates a ValuesRelNode, which is Calcite's relational algebra representation of a query that returns one row with one column holding the value 1.

2. Recommended RelBuilder API for BigQuery Scenario #

When working with BigQuery, you don't need a specialized BigQuery-only RelBuilder API—you'll use core RelBuilder methods, but ensure your RelBuilder is initialized with a configuration that uses the BigQueryRelDialect.

For the SELECT 1 case specifically:

• Use the RelBuilder.values() method. This creates a ValuesRelNode, which the BigQuery dialect will correctly translate into valid BigQuery SQL (either as SELECT 1 or an equivalent VALUES (1) query, which BigQuery supports natively).

This works because BigQuery handles value-based queries seamlessly, and Calcite's BigQuery dialect knows how to map the ValuesRelNode to proper BigQuery syntax.

内容的提问来源于stack exchange，提问作者justAbit