Function pi 

pub fn pi<'a, V>() -> SQLExpr<'a, V, <V::DialectMarker as DialectTypes>::Double, NonNull, Scalar>
where
    V: SQLParam + 'a,
    V::DialectMarker: MathExt + PiSupport,

PI - returns the mathematical constant pi (PostgreSQL and MySQL).

Example

use drizzle_core::expr::pi;

// SELECT PI()
let pi_val = pi::<PostgresValue>();