SET TRANSACTION

SET TRANSACTION 语句用于在 GLOBALSESSION 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
SETVariableAssignmentListPASSWORDFORUsername=PasswordOptGLOBALSESSIONTRANSACTIONTransactionCharsCONFIGIdentifierstringLitConfigItemNameEqOrAssignmentEqSetExpr
TransactionChars
ISOLATIONLEVELIsolationLevelREADWRITEREADONLYAsOfClause
IsolationLevel
REPEATABLEREADREADCOMMITTEDUNCOMMITTEDSERIALIZABLE
AsOfClause
ASOFTIMESTAMPExpression

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-UNCOMMITTEDSERIALIZABLE
  • 通过快照隔离 (Snapshot Isolation) 技术,实现乐观事务的 REPEATABLE-READ 隔离级别,和 MySQL 兼容。
  • 在悲观事务中,TiDB 支持与 MySQL 兼容的 REPEATABLE-READREAD-COMMITTED 两种隔离级别。具体描述详见 Isolation Levels

另请参阅

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