查看隔离级别：select @@transaction_isolation;

    验证：read uncommitted
    set global transaction isolation level read uncommitted;

    右表使用了start transaction，还没有commit左表就已经可以查询了
    image.png

    验证：read committed

    set global transaction isolation level read committed;
    只能提交之后才能查询到
    image.png

    验证：repeatable read

    set global transaction isolation level repeatable read;
    左方永远都是读取最开始的信息，就算右方创建提交了，左方也还是读不到
    image.png

    验证：serializable

    set global transaction isolation level repeatable read;
    左边只要不输入提交，右边的查询就会进入卡顿
    image.png