Function date_part_to_sql

datafusion/sql/src/unparser/utils.rs:444–520

Converts a date_part function to SQL, tailoring it to the supported date field extraction style.

(
    unparser: &Unparser,
    style: DateFieldExtractStyle,
    date_part_args: &[Expr],
)

/// Converts a date_part function to SQL, tailoring it to the supported date field extraction style.
pub(crate) fn date_part_to_sql(
    unparser: &Unparser,
    style: DateFieldExtractStyle,
    date_part_args: &[Expr],
) -> Result<Option<ast::Expr>> {
    match (style, date_part_args.len()) {
        (DateFieldExtractStyle::Extract, 2) => {
            let date_expr = unparser.expr_to_sql(&date_part_args[1])?;
            if let Expr::Literal(ScalarValue::Utf8(Some(field)), _) = &date_part_args[0] {
                let field = match field.to_lowercase().as_str() {
                    "year" => ast::DateTimeField::Year,
                    "month" => ast::DateTimeField::Month,
                    "day" => ast::DateTimeField::Day,
                    "hour" => ast::DateTimeField::Hour,
                    "minute" => ast::DateTimeField::Minute,
                    "second" => ast::DateTimeField::Second,
                    _ => return Ok(None),
                };

                return Ok(Some(ast::Expr::Extract {
                    field,
                    expr: Box::new(date_expr),
                    syntax: ast::ExtractSyntax::From,
                }));
            }
        }
        (DateFieldExtractStyle::Strftime, 2) => {
            let column = unparser.expr_to_sql(&date_part_args[1])?;

            if let Expr::Literal(ScalarValue::Utf8(Some(field)), _) = &date_part_args[0] {
                let field = match field.to_lowercase().as_str() {
                    "year" => "%Y",
                    "month" => "%m",
                    "day" => "%d",
                    "hour" => "%H",
                    "minute" => "%M",
                    "second" => "%S",
                    _ => return Ok(None),
                };

                return Ok(Some(ast::Expr::Function(ast::Function {
                    name: ast::ObjectName::from(vec![ast::Ident {
                        value: "strftime".to_string(),
                        quote_style: None,
                        span: Span::empty(),
                    }]),
                    args: ast::FunctionArguments::List(ast::FunctionArgumentList {
                        duplicate_treatment: None,
                        args: vec![
                            ast::FunctionArg::Unnamed(ast::FunctionArgExpr::Expr(
                                ast::Expr::value(ast::Value::SingleQuotedString(
                                    field.to_string(),
                                )),
                            )),
                            ast::FunctionArg::Unnamed(ast::FunctionArgExpr::Expr(column)),
                        ],
                        clauses: vec![],
                    }),