Expressions

Overview

The Expr type is the versioned expression AST used throughout DataFrame, GroupedDataFrame, and streaming operators. Build expressions using the provided constructor functions rather than constructing Expr directly.

Column and Literal

Function	Signature	Description
col	col(name: &str) -> Expr	Reference a column by name.
lit	lit(value: impl Into<Literal>) -> Expr	Create a literal constant expression.
expr	expr(sql: &str) -> Result<Expr>	Parse a SQL expression string into an Expr.

Aggregate Functions

Function	Signature	Description
count	count(expr: Expr) -> Expr	Count non-null values.
count_all	count_all() -> Expr	Count all rows (COUNT(*)).
sum	sum(expr: Expr) -> Expr	Sum of numeric values.
avg	avg(expr: Expr) -> Expr	Arithmetic mean.
min	min(expr: Expr) -> Expr	Minimum value.
max	max(expr: Expr) -> Expr	Maximum value.
function	function(name: &str, args: Vec<Expr>) -> Expr	Call a named SQL function or registered UDF.

Expr Methods

Method	Description
.alias(name)	Give an output alias to the expression.
.gt(rhs)	Greater-than comparison.
.lt(rhs)	Less-than comparison.
.eq(rhs)	Equality comparison.
.and(rhs)	Boolean AND.
.or(rhs)	Boolean OR.
.not()	Boolean NOT.
.cast(data_type)	Explicit type cast.
.is_null()	IS NULL predicate.
.is_not_null()	IS NOT NULL predicate.
.asc()	Wrap in ascending sort order.
.desc()	Wrap in descending sort order.

Example

use krishiv_api::{col, lit, sum, count_all};

let df = session.sql("SELECT * FROM sales").await?;
let result = df
    .filter(col("amount").gt(lit(100i64)))?
    .group_by(vec![col("region")])?
    .agg(vec![
        sum(col("amount")).alias("total"),
        count_all().alias("count"),
    ])?
    .sort(vec![col("total").desc()])?
    .collect().await?;