存储过程中的 MySQL 案例：错误代码：1064

Question

table: orders (Fields: customerNumber, status) requirement: accepts customer number and returns the total number of orders that were shipped, canceled, resolved, and disputed. more information: https://www.mysqltutorial.org/mysql-stored-procedures-return-multiple-values/

## I am trying to implement this requirement using case when. the code is below: 
## using MySQLWorkBench
delimiter //
create procedure get_order_number_by_status(
    in cnumber int
    , out shipped int
    , out cancelled int 
    , out resolved int 
    , out disputed int 
    )
begin
    select case o.status  ## Error: "select is not valid at this position for...
        when 'Shipped' then  shipped :=shipped +1
        when 'Cancelled' then  cancelled :=cancelled +1
        when 'Resolved' then  resolved :=resolved +1
        when 'Disputed' then  disputed :=disputed +1
        else null
        end
    from customers c join orders o
    on c.customernumber = o.customernumber
    where c.customernumber = cnumber;
end //

I cannot resolve this issue, need help on this..

Answer 1

Local variables cannot be used by such way. Only user-defined variables allows inline assignement.

create procedure get_order_number_by_status(
    in cnumber int
    , out shipped int
    , out cancelled int 
    , out resolved int 
    , out disputed int 
    )
begin
    select case o.status 
        when 'Shipped' then  @shipped := @shipped +1
        when 'Cancelled' then  @cancelled := @cancelled +1
        when 'Resolved' then  @resolved := @resolved +1
        when 'Disputed' then  @disputed := @disputed +1
        else null
        end
    from customers c join orders o
    on c.customernumber = o.customernumber
    CROSS JOIN (SELECT @shipped:=0, @cancelled:=0, @resolved:=0, @disputed:=0) init
    where c.customernumber = cnumber;
    SET shipped := @shipped;
    SET cancelled := @cancelled;
    SET resolved := @resolved;
    SET disputed := @disputed;
end

fiddle

PS. Why not simple

create procedure get_order_number_by_status(
    in cnumber int
    , out shipped int
    , out cancelled int 
    , out resolved int 
    , out disputed int 
    )

    select SUM(o.status = 'Shipped'),
           SUM(o.status = 'Cancelled'),
           SUM(o.status = 'Resolved'),
           SUM(o.status = 'Disputed')
    INTO shipped, cancelled, resolved, disputed
    from customers c join orders o
    on c.customernumber = o.customernumber
    where c.customernumber = cnumber
    GROUP BY o.status;

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