SET TRANSACTION

SET TRANSACTION 语句用于在 GLOBAL 或 SESSION 的基础上更改当前的隔离级别，是 SET transaction_isolation ='new-value' 的替代语句，提供 MySQL 和 SQL 标准的兼容性。

语法图

SetStmt:

TransactionChar:

IsolationLevel:

示例

mysql> SHOW SESSION VARIABLES like 'transaction_isolation';
+-----------------------+-----------------+
| Variable_name         | Value           |
+-----------------------+-----------------+
| transaction_isolation | REPEATABLE-READ |
+-----------------------+-----------------+
 row in set (0.00 sec)
mysql> SET SESSION TRANSACTION ISOLATION LEVEL READ COMMITTED;
Query OK, 0 rows affected (0.00 sec)
mysql> SHOW SESSION VARIABLES like 'transaction_isolation';
+-----------------------+----------------+
| Variable_name         | Value          |
+-----------------------+----------------+
| transaction_isolation | READ-COMMITTED |
+-----------------------+----------------+
 row in set (0.01 sec)
mysql> SET SESSION transaction_isolation = 'REPEATABLE-READ';
Query OK, 0 rows affected (0.00 sec)
mysql> SHOW SESSION VARIABLES like 'transaction_isolation';
+-----------------------+-----------------+
| Variable_name         | Value           |
+-----------------------+-----------------+
| transaction_isolation | REPEATABLE-READ |
+-----------------------+-----------------+
 row in set (0.00 sec)

MySQL 兼容性

• TiDB 支持仅在语法中将事务设置为只读的功能。
• 不支持隔离级别 READ-UNCOMMITTED 和 SERIALIZABLE。
• 隔离级别 REPEATABLE-READ 在技术上属于快照隔离（Snapshot Isolation）。在 TiDB 中称为 REPEATABLE-READ 是为了和 MySQL 保持一致。

另请参阅

• SET [GLOBAL|SESSION]
• Isolation Levels