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
SHOW SESSION VARIABLES like 'transaction_isolation';
+-----------------------+-----------------+
| Variable_name | Value |
+-----------------------+-----------------+
| transaction_isolation | REPEATABLE-READ |
+-----------------------+-----------------+
1 row in set (0.00 sec)
SET SESSION TRANSACTION ISOLATION LEVEL READ COMMITTED;
Query OK, 0 rows affected (0.00 sec)
SHOW SESSION VARIABLES like 'transaction_isolation';
+-----------------------+----------------+
| Variable_name | Value |
+-----------------------+----------------+
| transaction_isolation | READ-COMMITTED |
+-----------------------+----------------+
1 row in set (0.01 sec)
SET SESSION transaction_isolation = 'REPEATABLE-READ';
Query OK, 0 rows affected (0.00 sec)
SHOW SESSION VARIABLES like 'transaction_isolation';
+-----------------------+-----------------+
| Variable_name | Value |
+-----------------------+-----------------+
| transaction_isolation | REPEATABLE-READ |
+-----------------------+-----------------+
1 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。