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use self::private::SqlOrdAggregate;
use crate::expression::functions::sql_function;
sql_function! {
/// Represents a SQL `MAX` function. This function can only take types which are
/// ordered.
///
/// # Examples
///
/// ```rust
/// # include!("../../doctest_setup.rs");
/// # use diesel::dsl::*;
/// #
/// # fn main() {
/// # use schema::animals::dsl::*;
/// # let connection = &mut establish_connection();
/// assert_eq!(Ok(Some(8)), animals.select(max(legs)).first(connection));
/// # }
#[aggregate]
fn max<ST: SqlOrdAggregate>(expr: ST) -> ST::Ret;
}
sql_function! {
/// Represents a SQL `MIN` function. This function can only take types which are
/// ordered.
///
/// # Examples
///
/// ```rust
/// # include!("../../doctest_setup.rs");
/// # use diesel::dsl::*;
/// #
/// # fn main() {
/// # use schema::animals::dsl::*;
/// # let connection = &mut establish_connection();
/// assert_eq!(Ok(Some(4)), animals.select(min(legs)).first(connection));
/// # }
#[aggregate]
fn min<ST: SqlOrdAggregate>(expr: ST) -> ST::Ret;
}
mod private {
use crate::sql_types::{IntoNullable, SingleValue, SqlOrd, SqlType};
pub trait SqlOrdAggregate: SingleValue {
type Ret: SqlType + SingleValue;
}
impl<T> SqlOrdAggregate for T
where
T: SqlOrd + IntoNullable + SingleValue,
T::Nullable: SqlType + SingleValue,
{
type Ret = T::Nullable;
}
}