Oracle|MySQL|SQL Server的事務隔離級別

支持的隔離級別及默認值

	Oracle	MySQL	SQL Server
支持	Read Committed提交讀 Serializable可串行化	Read Uncommitted未提交讀 Read Committed提交讀 Repeatable Read可重複讀 Serializable可串行化	Read Uncommitted未提交讀 Read Committed提交讀 Repeatable Read可重複讀 Serializable可串行化 Snapshot快照 Read Committed Snapshot已經提交讀隔離
默認	Read Commit提交讀	Repeatable Read可重複讀	Read Commit提交讀

 

設置語句

Oracle

-- 設置提交讀
SET TRANSACTION ISOLATION LEVEL READ COMMITTED;
-- 設置可串行化，SYS用戶不支持該操作
SET TRANSACTION ISOLATION LEVEL SERIALIZABLE;

MySQL

MySQL的設置可以分爲系統級別（GLOBAL）和會話級別（SESSION）

-- 未提交讀
SET GLOBAL|SESSION TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;
-- 提交讀
SET GLOBAL|SESSION TRANSACTION ISOLATION LEVEL READ COMMITTED;
-- 可重複讀
SET GLOBAL|SESSION TRANSACTION ISOLATION LEVEL REPEATABLE READ;
-- 可串行化
SET GLOBAL|SESSION TRANSACTION ISOLATION LEVEL SERIALIZABLE;

SQL Server

-- 未提交讀
SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;
-- 提交讀
SET TRANSACTION ISOLATION LEVEL READ COMMITTED;
-- 可重複讀
SET TRANSACTION ISOLATION LEVEL REPEATABLE READ;
-- 可串行化
SET TRANSACTION ISOLATION LEVEL SERIALIZABLE;
-- 快照
ALTER DATABASE TEST SET ALLOW_SNAPSHOT_ISOLATION ON;
-- 已經提交讀隔離
ALTER DATABASE TEST SET READ_COMMITTED_SNAPSHOT ON;

查詢語句

Oracle

SELECT S.SID,S.SERIAL#,
      CASE BITAND(T.FLAG,POWER(2,28)) 
      WHEN 0 THEN 'READ COMMITTED' ELSE 'SERIALIZABLE' END AS ISOLATION_LEVEL
FROM V$TRANSACTION T 
JOIN V$SESSION S
ON T.ADDR = S.TADDR AND S.SID = SYS_CONTEXT('USERENV','SID')

MySQL

-- 查詢當前會話的事務隔離級別
SELECT @@TX_ISOLATION;
-- 查詢數據庫系統的事務隔離級別
SELECT @@GLOBAL.TX_ISOLATION;
-- 兩者同時查詢
SELECT @@TX_ISOLATION AS current_session_isolation_level,
    @@GLOBAL.TX_ISOLATION as global_isolation_level

SQL Server

DBCC USEROPTIONS