读未提交
建表
CREATE TABLE user (id int(11) NOT NULL,name varchar(20) DEFAULT NULL,age int(11) NOT NULL,
PRIMARY KEY (id),
UNIQUE KEY name (name)
)
读未提交
session 1: SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;
session 1:begin;
session 2:begin;
session 2:insert into user(id,name,age) values(1, “张三”, 20);
session 1: select * from user; (脏读)
session 2: rollback;
session 1: select * from user;
Empty set (0.00 sec)
session 1: commit;
读已提交
session 1: SET TRANSACTION ISOLATION LEVEL READ COMMITTED;
session 1: begin
session 2: begin;
session 2: insert into user(id,name,age) values(1, “张三”, 20);
session 1: select * from user;
Empty set (0.00 sec)
session 2: commit;
session 1: select * from user;
可重复读
快照读与当前读
session 1: SET TRANSACTION ISOLATION LEVEL REPEATABLE READ;
session 1: begin;
session 2: begin;
session 2: insert into user(id,name,age) values(3, “李四”, 20);
session 1:select * from user;(快照读)
session 2: commit;
session 1: select * from user;
session 1: select * from user for update;(直接读)
快照建立在第一次执行查询语句的时候
session 1: begin;
session 2: begin;
session 3: begin;
session 1: select * from user;
session 3:update user set age = 21 where id = 3;
session 3:commit;
session 1: select * from user;
session2 : select * from user;