Principle:Eventual Inc Daft SQL Expression Building
| Knowledge Sources | |
|---|---|
| Domains | Data_Engineering, SQL |
| Last Updated | 2026-02-08 00:00 GMT |
Overview
Technique for constructing DataFrame expressions using SQL syntax.
Description
SQL expression building parses SQL expression strings into Daft Expression objects, enabling SQL syntax for computed columns, filters, and aggregations within the DataFrame API. This bridges the gap between SQL and the programmatic DataFrame API, allowing users to mix SQL expressions with Python-native DataFrame operations. Some DataFrame methods like where automatically call sql_expr when given a string argument.
Usage
Use SQL expression building when you want to use SQL syntax for expressions within DataFrame operations. Particularly useful for CASE WHEN expressions, complex arithmetic, and when SQL syntax is more readable than chained method calls.
Theoretical Basis
SQL expression parsing converting SQL syntax into the same expression tree used by the DataFrame API:
sql_expr("col1 + col2")
-> Parse SQL expression string
-> Build Rust expression AST
-> Wrap as Python Expression object
-> Same type as col("col1") + col("col2")
The resulting Expression is fully interchangeable with expressions built through the Python API and benefits from the same query optimization.