MySql assigning a select - mysql

Question

I am trying to create a MySql function that will tell me how many orders(comanda) have been placed by a client(whose id i will provide as a parameter).
However, I am getting a syntax error that says counter(my decared variable) is not valid at this position, expecting an identifier.
I split the declaration and both assignments of the value just to be sure that this is not the reason for the error. The error triggers at the last assignment of the select.
Can anybody explain what I am doing wrong? Thank you!
create table client
(id int primary key auto_increment,
nume varchar(50),
prenume varchar(50),
oras varchar(50),
judet varchar(50),
strada varchar(50),
cod_postal varchar(50),
nr_tel varchar(50),
email varchar(50)
);
create table comanda
(id int primary key auto_increment,
data_plasare date,
metoda_livrare enum('ridicare personala','livrare la domiciliu','easy box'),
metoda_plata enum('numerar','card la ghiseu','online cu cardul','transfer bancar','PayPal','rate'),
id_client int
);
alter table comanda
add foreign key (id_client) references client(id);
delimiter //
create function clienti_multiple_comenzi(p_id_client int)
returns int
begin
declare counter int;
set counter = 0;
set counter = select count(id)
from comanda
where id_client = p_id_client;
return counter;
end;
// delimiter ;