Function concat 

pub fn concat<'a, V, E1, E2>(
    expr1: E1,
    expr2: E2,
) -> SQLExpr<'a, V, <V::DialectMarker as DialectTypes>::Text, <E1::Nullable as NullOr<E2::Nullable>>::Output, <E1::Aggregate as AggOr<E2::Aggregate>>::Output>
where
    V: SQLParam + 'a,
    E1: Expr<'a, V>,
    E1::SQLType: Textual,
    E2: Expr<'a, V>,
    E2::SQLType: Textual,
    E1::Nullable: NullOr<E2::Nullable>,
    E2::Nullable: Nullability,
    E2::Aggregate: AggregateKind,
    E1::Aggregate: AggOr<E2::Aggregate>,

Concatenate two string expressions using || operator.

Nullability follows SQL concatenation rules: if either input is nullable, the result is nullable. string_concat is a compatibility alias.

Type Safety

// ✅ OK: Both are Text
concat(users.first_name, users.last_name);

// ✅ OK: Text with string literal
concat(users.first_name, " ");

// ❌ Compile error: Int is not Textual
concat(users.id, users.name);

Example

use drizzle_core::expr::concat;

// SELECT users.first_name || ' ' || users.last_name
let full_name = concat(concat(users.first_name, " "), users.last_name);