You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: legacy_compiler.rs
    path of file: ./repos/cube/rust/cubesql/cubesql/src/compile
    
    the code of the file until where you have to start completion: use crate::{
    compile::{
        builder::{CompiledQueryFieldMeta, QueryBuilder},
        context::{QueryContext, Selection},
        error::CompilationError,
        CompilationResult,
    },
    sql::ColumnType,
    transport::{V1CubeMetaDimensionExt, V1CubeMetaMeasureExt, V1CubeMetaSegmentExt},
};
use chrono::{
    DateTime, Datelike, Duration, NaiveDate, NaiveDateTime, SecondsFormat, TimeZone, Utc,
};
use cubeclient::models::{V1LoadRequestQueryFilterItem, V1LoadRequestQueryTimeDimension};
use log::{debug, trace};
use serde_json::json;
use sqlparser::ast;

fn compile_select_expr(
    expr: &ast::Expr,
    ctx: &mut QueryContext,
    builder: &mut QueryBuilder,
    mb_alias: Option<String>,
) -> CompilationResult<()> {
    let selection =
        ctx.compile_selection_from_projection(expr)?
            .ok_or(CompilationError::unsupported(format!(
                "Unknown expressio
    
    fn parse_expr_from_projection(query: &String, db: DatabaseProtocol) -> ast::Expr {
        let stmt = parse_sql_to_statement(&query, db, &mut None).unwrap();
        match stmt {
            ast::Statement::Query(query) => match &query.body {
                ast::SetExpr::Select(select) => {
                    if select.projection.len() == 1 {
                        match &select.projection[0] {
                            ast::SelectItem::UnnamedExpr(expr) => {
                                return expr.clone();
                            }
                            ast::SelectItem::ExprWithAlias { expr, .. } => {
                                return expr.clone();
                            }
                            _ => panic!("err"),
                        };
                    } else {
                        panic!("err");
                    }
                }
                _ => panic!("err"),
            },
            _ => panic!("err"),
        }
    }