Mysql存储过程、触发器、事件调度器使用入门指南

create procedure test()
begin
    select * from users;
end;

call test();   

create procedure test()
begin

  -- 使用 declare语句声明一个变量
  declare username varchar(32) default '';
  
  -- 使用set语句给变量赋值
  set username='xiaoxiao';
  
  -- 将users表中id=1的名称赋值给变量username
  select name into username from users where id=1;
  
  -- 返回变量
  select username;
end;

 create procedure test()
    begin
      declare userscount int default 0; -- 用户表中的数量
      begin
            select count(*) into userscount from users;
            select userscount; -- 返回用户表中的数量
      end;
      begin 
        declare maxmoney int default 0; -- 最大金额
        select max(money) into maxmoney from orders;
        select userscount,maxmoney; -- 返回用户表中的数量、最大金额
       end;
    end;

create procedure 名称([IN|OUT|INOUT] 参数名 参数数据类型 )
begin
......
end

 create procedure test(userId int)
    begin
        declare username varchar(32) default '';
        select name into username from users where id=userId;
        select username;
    end;

create procedure test(in userId int,out username varchar(32))
   begin
     select name into username from users where id=userId;
   end;

create procedure test6(inout userId int,inout username varchar(32))
begin
    set userId=2;
    set username='';
    select id,name into userId,username from users where id=userId;
end;

if() then...
elseif() then...
else ...
end if;

create procedure test(in userid int)
begin
   declare my_status int default 0;
   select status into my_status from users where id=userid;
   
   if(my_status=1)
   then 
       update users set score=score+10 where id=userid;
   elseif(my_status=2)
   then 
       update users set score=score+20 where id=userid;
   else 
       update users set score=score+30 where id=userid;
   end if;
end;

while(表达式) do 
   ......  
end while;

create procedure test()
begin
  declare i int default 0;
  while(i<10) do 
     begin 
        select i;
        set i=i+1;
        insert into test1(id) values(i);
     end;
  end while;
end;

repeat...until...end repeat;

create procedure test()
begin
    declare i int default 0;
    repeat 
     begin 
        select i;
        set i=i+1;
        insert into test1(id) values(i);
     end;
    until i>=10 -- 如果i>=10,则跳出循环
    end repeat;
end;

case ...
when ... then....
when.... then....
else ... 
end case;

 create procedure testcate(userid int)
    begin 
        declare my_status int default 0;
        select status into my_status from users where id=userid;
 
        case my_status
            when 1 then update users set score=10 where id=userid;
            when 2 then update users set score=20 where id=userid;
            when 3 then update users set score=30 where id=userid;
            else update users set score=40 where id=userid;
        end case;
    end;

declare 变量名 cursor ... -- 创建一个游标变量
close 变量名; -- 关闭游标

create procedure test()
    begin
        declare stopflag int default 0;
        declare username VARCHAR(32);
        declare username_cur cursor for select name from users where id%2=0;
        -- 游标变量username_cur保存了查询的临时结果，即结果集
        -- 在游标变量中数据的结尾，将变量stopflag设置为1，用于循环中判断是否结束
        declare continue handler for not found set stopflag=1;
 
        open username_cur; -- 打卡游标
        fetch username_cur into username; -- 游标向前走一步，取出一条记录放到变量username中
        while(stopflag=0) do -- 如果游标还没有结尾，就继续
            begin 
                -- 在用户名前门拼接 '_cur' 字符串
                update users set name=CONCAT(username,'_cur') where name=username;
                fetch username_cur into username;-- 游标向前走一步，取出一条记录放到变量username中
            end;
        end while; -- 结束循环
        close username_cur; -- 关闭游标
    end;

-- 创建函数
create function 函数名(参数) returns 返回类型；
-- 函数体
begin ...... end；
-- 指定函数的返回值
returns
--函数调用
select 函数名()。

create function getusername(userid int) returns varchar(32)
    reads sql data  -- 从数据库中读取数据，但不修改数据
    begin
        declare username varchar(32) default '';
        select name into username from users where id=userid;
        return username;
    end;

create trigger tr_users_insert after insert on users
    for each row 
    begin 
        insert into oplog(userid,username,action,optime)
        values(NEW.userid,NEW.name,'insert',now());
    end;

create trigger tr_users_delete before delete on users
    for each row 
    begin 
        insert into oplog(userid,username,action,optime)
        values(OLD.id,OLD.name,'delete',now());
    end;

SET GLOBAL event_scheduler = 1;
-- 或者
SET GLOBAL event_scheduler = on;

--查看开启情况
show variables like '%event_scheduler%';

create event[IF NOT EXISTS]event_name -- 创建使用create event
    ON SCHEDULE schedule -- on schedule 什么时候来执行
    [ON COMPLETION [NOT] PRESERVE] -- 调度计划执行完成后是否还保留
    [ENABLE | DISABLE] -- 是否开启事件，默认开启
    [COMMENT 'comment'] -- 事件的注释
    DO sql_statement; -- 这个调度计划要做什么？

-- 存储过程
create procedure test()
        begin 
            insert into lottery(num1,num2,num3,ctime)
            select FLOOR(rand()*9)+1,FLOOR(rand()*9)+1,FLOOR(rand()*9)+1,now();
        end;

-- 事件
create event if not exists test_event -- 创建一个事件
        on schedule every  3 minute -- on schedule 每三分钟执行一次
        on completion preserve 
        do call test;  --调用存储过程