Analysis of MYSQLREPEATABLE-READ isolation level

The REPEATABLE-READ can be read again, and the content of the select table in the setautocommit0 or STARTTRANSACTION state will not change. This isolation level may cause the read to have been modified. For example, in session 1, read a field and a line a1. In Session 2, modify this line a0, and submit the word "update" in session 1.

The REPEATABLE-READ can be read repeatedly, and the contents of the select table in the set autocommit = 0 or start transaction state will not change. This isolation level may cause the read to have been modified. For example, in session 1, read a field and a = 1. In Session 2, modify the field a = 0, and submit the word "update" in session 2.

The REPEATABLE-READ can be read repeatedly, and the contents of the select table in the set autocommit = 0 or start transaction state will not change. This isolation level may cause the read to have been modified.

For example:

Session 1 reads a field with a line a = 1

In Session 2, this field is modified to a = 0 and submitted.

When the field a = 0 is updated in session 1, it will find that the number of affected rows is 0, so that you can determine whether the modification is successful based on whether the number of affected rows is 0 or 1!

This is useful in some programs!

Session 1:

Mysql> set autocommit = 0;
Query OK, 0 rows affected (0.00 sec)

Mysql> select * from test. dd where id = 1;
+ ---- + ------ +
| Id | aa |
+ ---- + ------ +
| 1 | 2 |
+ ---- + ------ +
1 row in set (0.00 sec)

Session 2:

Mysql> update test. dd set aa = 1 where id = 1;
Query OK, 1 row affected (0.09 sec)
Rows matched: 1 Changed: 1 Warnings: 0

Session 3:

Mysql> select * from test. dd where id = 1;
+ ---- + ------ +
| Id | aa |
+ ---- + ------ +
| 1 | 2 |
+ ---- + ------ +
1 row in set (0.00 sec)

Mysql> update test. dd set aa = 1 where id = 1;
Query OK, 0 rows affected (0.00 sec)
Rows matched: 1 Changed: 0 Warnings: 0

The number of affected rows here is 0. We can determine whether the update is successful based on this value. This is useful when you need to change the status bit of some rows!