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  • MySQL 自增列插入0值的方法

    在将数据库从MSSQL迁移到MySQL的过程中,基于业务逻辑的要求,需要在MySQL的自增列插入0值。在MSSQL中是这样完成的:

      string sql;

    sql = " set identity_insert dbo.AppUsers on "
         + " insert dbo.AppUsers (Id, IsLocked, IsMustChangeLocalPassword, IsAvailable, Name, Sequence, CreatedBy, CreatedTime, UpdatedBy, UpdatedTime) "
         + " values (0, 1, 0, 0, '[SYSTEM]', 0, 0, GetDate(), 0, GetDate()) "
         + " set identity_insert dbo.AppUsers off "
         + " DBCC CHECKIDENT ('dbo.AppUsers', RESEED, 0) ";

      db.Database.ExecuteSqlCommand(sql);

    MySQL官方文档中是这样写的:

    NO_AUTO_VALUE_ON_ZERO affects handling of AUTO_INCREMENT columns. Normally, you generate the next sequence number for the column by inserting either NULL or 0 into it. NO_AUTO_VALUE_ON_ZERO suppresses this behavior for 0 so that only NULL generates the next sequence number.
    This mode can be useful if 0 has been stored in a table's AUTO_INCREMENT column. (Storing 0 is not a recommended practice, by the way.) For example, if you dump the table with mysqldump and then reload it, MySQL normally generates new sequence numbers when
    it encounters the 0 values, resulting in a table with contents different from the one that was dumped. Enabling NO_AUTO_VALUE_ON_ZERO before reloading the dump file solves this problem. mysqldump now automatically includes in its output a statement that enables NO_AUTO_VALUE_ON_ZERO, to avoid this problem.

    大致的意思是说:NO_AUTO_VALUE_ON_ZERO会影响自增列,一般情况下,获得下一个序列值的方法是对自增列插入0或者NULL值。NO_AUTO_VALUE_ON_ZERO会改变这个缺省的行为,使得只有插入NULL值才能获取下一个序列值。这种方式对于要将0值插入自增列是有用的。(顺便指出,0值是不推荐使用在自增列的)例如,如果你使用mysqldump备份数据表然后再恢复它,MySQL一般情形下会0值自动产生新的序列值,结果是造成从备份恢复数据错误。在恢复数据前,启用NO_AUTO_VALUE_ON_ZERO可以解决这个问题。mysqldump现在会自动在输出的语句中包含NO_AUTO_VALUE_ON_ZERO来解决这个问题。

    在MySQL中需要这样:

      sql = " SET SESSION sql_mode='NO_AUTO_VALUE_ON_ZERO'; insert AppUsers (Id, IsLocked, IsMustChangeLocalPassword, IsAvailable, Name, Sequence, CreatedBy, CreatedTime, UpdatedBy, UpdatedTime) "
          + " values (0, 1, 0, 0, '[SYSTEM]', 0, 0, CURRENT_TIMESTAMP, 0, CURRENT_TIMESTAMP) ";

    至此问题解决。

    后记:

    由于业务逻辑需要,在自增列会存在0值,为了在Windows平台和Linux平台的MySQL之间复制数据,增加全局变量设置,在my.ini和my.cnf中分别添加NO_AUTO_VALUE_ON_ZERO设置到sql-mode行,例如:

    //my.ini 该文件在Windows7或Windows2008操作系统中位于 C:\ProgramData\MySQL\MySQL Server 5.6 目录下(采用MSI安装方式)
    # Set the SQL mode to strict sql-mode
    ="STRICT_TRANS_TABLES,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION,NO_AUTO_VALUE_ON_ZERO"

    重启MySQL服务后,查看sql-mode全局变量的办法:

    SELECT @@GLOBAL.sql_mode;

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  • 原文地址:https://www.cnblogs.com/jlzhou/p/2965384.html
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