Function fold_constant

nodedb-sql/src/planner/const_fold.rs:47–68

Fold a `SqlExpr` to a literal `SqlValue` at plan time, or return `None` if the expression depends on row/runtime state (column refs, subqueries, unknown functions, etc.).

(expr: &SqlExpr, registry: &FunctionRegistry)

/// `None` if the expression depends on row/runtime state (column refs,
/// subqueries, unknown functions, etc.).
pub fn fold_constant(expr: &SqlExpr, registry: &FunctionRegistry) -> Option<SqlValue> {
    match expr {
        SqlExpr::Literal(v) => Some(v.clone()),
        SqlExpr::UnaryOp {
            op: UnaryOp::Neg,
            expr,
        } => match fold_constant(expr, registry)? {
            SqlValue::Int(i) => Some(SqlValue::Int(-i)),
            SqlValue::Float(f) => Some(SqlValue::Float(-f)),
            SqlValue::Decimal(d) => Some(SqlValue::Decimal(-d)),
            _ => None,
        },
        SqlExpr::BinaryOp { left, op, right } => {
            let l = fold_constant(left, registry)?;
            let r = fold_constant(right, registry)?;
            fold_binary(l, *op, r)
        }
        SqlExpr::Function { name, args, .. } => fold_function_call(name, args, registry),
        SqlExpr::Cast { expr, to_type } => fold_cast(fold_constant(expr, registry)?, to_type),
        _ => None,
    }
}

/// Fold a CAST at plan time. Only applies when the inner expression is already
/// a constant. The `to_type` string comes from sqlparser's `format!("{data_type}")`