MySQL游标解析

While循环

-- MySQL游标只能用于存储过程和函数-- 使用过程 声明、打开游标、使用游标、关闭游标-- 如果未明确关闭游标，END时会自动关闭-- https://dev.mysql.com/doc/refman/8.0/en/error-handling.htmldrop PROCEDURE if exists process_user;create procedure process_user()begin

-- Declare local variables

declare done boolean default true; declare user_id int; declare user_info varchar(50);

-- Declare the cursor

declare cursor_user cursor for select id, user_name from sys_user;

-- Declare continue handler

declare continue handler for sqlstate '02000' set done=false;

-- Create a table to store the results;

create table if not exists process_user_result(user_id int, user_name varchar(50));

-- Open the cursor

open cursor_user;

-- Repeat through all rows

repeat

fetch cursor_user into user_id, user_info;

if done then

insert into process_user_result(user_id, user_name)

values(user_id, user_info); end if;

until (not done) end repeat;

-- Close the cursor

close cursor_user;end;call process_user();

Repeat循环

drop PROCEDURE if exists process_user;create procedure process_user()begin

-- Declare local variables

declare done boolean default true; declare user_id int; declare user_info varchar(50);

-- Declare the cursor

declare cursor_user cursor for select id, user_name from sys_user;

-- Declare continue handler

declare continue handler for not found set done=false;

-- Create a table to store the results;

create table if not exists process_user_result(user_id int, user_name varchar(50));

-- Open the cursor

open cursor_user;

-- Loop through all rows

fetch cursor_user into user_id, user_info;

while done do

insert into process_user_result(user_id, user_name)

values(user_id, user_info);

fetch cursor_user into user_id, user_info; end while;

-- Close the cursor

close cursor_user;end;call process_user();

Loop循环

drop PROCEDURE if exists process_user;create procedure process_user()begin

-- Declare local variables

declare done boolean default true; declare user_id int; declare user_info varchar(50);

-- Declare the cursor

declare cursor_user cursor for select id, user_name from sys_user;

-- Declare continue handler

declare continue handler for not found set done=false;

-- Create a table to store the results;

create table if not exists process_user_result(user_id int, user_name varchar(50));

-- Open the cursor

open cursor_user;

-- Loop through all rows

read_loop:loop

fetch cursor_user into user_id, user_info;

if not done then

leave read_loop; end if; insert into process_user_result(user_id, user_name) values(user_id, user_info); end loop;

-- Close the cursor

close cursor_user;end;call process_user();