Implementation:Lance format Lance Java SqlExpressions

Knowledge Sources	Lance
Domains	Java_SDK, Dataset_Management
Last Updated	2026-02-08 19:33 GMT

Overview

Description

The SqlExpressions class represents a list of named SQL expressions for computed column generation. Each expression consists of a name (the target column name) and an expression (a SQL expression string that can reference existing columns in the dataset). The evaluated expression becomes the value of the new column.

The class uses an immutable outer container with an inner SqlExpression class that follows the JavaBean pattern (getter/setter). The Builder provides a fluent withExpression(name, expr) method that creates and appends SqlExpression entries incrementally.

Usage

Use SqlExpressions to define computed columns when adding new columns to a Lance dataset. Each expression is evaluated against existing dataset columns to produce new column values. This is commonly used with update or add-column operations.

Code Reference

Source Location

java/src/main/java/org/lance/schema/SqlExpressions.java

Signature

public class SqlExpressions {
    public List<SqlExpression> getSqlExpressions();

    public static class SqlExpression {
        public String getName();
        public void setName(String name);
        public String getExpression();
        public void setExpression(String expression);
    }

    public static class Builder {
        public Builder();
        public Builder withExpression(String name, String expr);
        public SqlExpressions build();
    }
}

Import

import org.lance.schema.SqlExpressions;
import org.lance.schema.SqlExpressions.SqlExpression;

I/O Contract

Builder Inputs

Parameter	Type	Required	Description
name	String	Yes	The name for the new computed column
expr	String	Yes	SQL expression string referencing existing dataset columns

Outputs

Method	Return Type	Description
getSqlExpressions()	List<SqlExpression>	The list of named SQL expressions

SqlExpression Properties

Property	Type	Description
name	String	Column name for the computed result
expression	String	SQL expression evaluated against existing columns

Usage Examples

// Define computed columns using SQL expressions
SqlExpressions expressions = new SqlExpressions.Builder()
    .withExpression("full_name", "first_name || ' ' || last_name")
    .withExpression("age_group", "CASE WHEN age < 18 THEN 'minor' ELSE 'adult' END")
    .withExpression("score_normalized", "score / 100.0")
    .build();

// Access individual expressions
for (SqlExpression expr : expressions.getSqlExpressions()) {
    System.out.println(expr.getName() + " = " + expr.getExpression());
}

Related Pages

• Lance_format_Lance_Java_UpdateOp -- Update operation that may use SQL expressions for column values
• Lance_format_Lance_Java_MergeOp -- Merge operation for adding new columns to datasets
• Lance_format_Lance_Java_ColumnAlteration -- Alters column properties rather than computing new values