FreeSql 中用于 SQL Server 的锁定选项枚举说明

示例：
FreeSql.Select().WithLock(SqlServerLock.ReadPast)
FreeSql.Select().WithLock(SqlServerLock.ReadPast | SqlServerLock.NoLock)

1. NoLock (1)

   • sql: SELECT TOP 1 ... FROM [tableName] WITH (NOLOCK)
   • 最低隔离级别，允许读取未提交数据
   • 完全忽略锁机制，可能读到脏数据，但性能最好

2. HoldLock (2)

   • sql: SELECT TOP 1 ... FROM [tableName] WITH (HOLDLOCK)
   • 持有共享锁直到事务结束
   • 防止其他事务修改已读取的数据

3. UpdLock (4)

   • sql: SELECT TOP 1 ... FROM [tableName] WITH (UPDLOCK)
   • 获取更新锁
   • 防止其他事务修改数据，但允许读取

4. RowLock (8)

   • sql: SELECT TOP 1 ... FROM [tableName] WITH (ROWLOCK)
   • 行级锁定
   • 最细粒度的锁定方式

5. ReadCommitted (16)

   • sql: SELECT TOP 1 ... FROM [tableName] WITH (READCOMMITTED)
   • 只读取已提交的数据
   • 防止脏读

6. ReadPast (32)

   • sql: SELECT TOP 1 ... FROM [tableName] WITH (READPAST)
   • 跳过被锁定的行
   • 用于读取未被锁定的行

7. ReadUnCommitted (64)

   • sql: SELECT TOP 1 ... FROM [tableName] WITH (READUNCOMMITTED)
   • 允许读取未提交数据
   • 功能类似于 NoLock

8. RepeaTableRead (256)

   • sql: SELECT TOP 1 ... FROM [tableName] WITH (REPEATABLEREAD)
   • 可重复读
   • 确保在事务期间读取的数据不会改变

9. PagLock (512)

   • sql: SELECT TOP 1 ... FROM [tableName] WITH (PAGLOCK)
   • 页级锁定
   • 锁定整个数据页

10. Serializable (1024)

    • sql: SELECT TOP 1 ... FROM [tableName] WITH (SERIALIZABLE)
    • 最高隔离级别
    • 完全串行化访问

11. TabLock (2048)

    • sql: SELECT TOP 1 ... FROM [tableName] WITH (TABLOCK)
    • 表级锁定
    • 锁定整个表

12. TabLockX (4096)

    • sql: SELECT TOP 1 ... FROM [tableName] WITH (TABLOCKX)
    • 排他表锁
    • 独占整个表的访问

13. XLock (8192)

    • sql: SELECT TOP 1 ... FROM [tableName] WITH (XLOCK)
    • 排他锁
    • 防止其他事务读取或修改数据

14. NoWait (16384)

    • sql: SELECT TOP 1 ... FROM [tableName] WITH (NOWAIT)
    • 如果无法立即获取锁则返回错误
    • 不等待锁的释放

参考：https://freesql.net/guide/select.html#sqlserver-withlock-withindex