详解MySQL存储过程参数有三种类型(in、out、inout)

drop procedure if exists pr_param_in;
create procedure pr_param_in
(
in id int -- in 类型的 MySQL 存储过程参数
)
begin
if (id is not null) then
set id = id + 1;
end if;
select id as id_inner;
end;
set @id = 10;
call pr_param_in(@id);
select @id as id_out;
mysql> call pr_param_in(@id);

drop procedure if exists pr_param_out;
create procedure pr_param_out
(
out id int
)
begin
select id as id_inner_1; -- id 初始值为 null
if (id is not null) then
set id = id + 1;
select id as id_inner_2;
else
select 1 into id;
end if;
select id as id_inner_3;
end;
set @id = 10;
call pr_param_out(@id);
select @id as id_out;
mysql> set @id = 10;
mysql>
mysql> call pr_param_out(@id);

drop procedure if exists pr_param_inout;
create procedure pr_param_inout
(
inout id int
)
begin
select id as id_inner_1; -- id 值为调用者传进来的值
if (id is not null) then
set id = id + 1;
select id as id_inner_2;
else
select 1 into id;
end if;
select id as id_inner_3;
end;
set @id = 10;
call pr_param_inout(@id);
select @id as id_out;
mysql> set @id = 10;
mysql>
mysql> call pr_param_inout(@id);