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关于MQT
创建MQT时如何选择使用maintained by system 还是by user ？
有啥依据吗？
MAINTAINED BY
Specifies whether the data in the materialized query table is maintained by the system, user, or replication tool. The default is SYSTEM.
SYSTEM
Specifies that the data in the materialized query table is maintained by the system.
USER
Specifies that the data in the materialized query table is maintained by the user. The user is allowed to perform update, delete, or insert operations against user-maintained materialized query tables. The REFRESH TABLE statement, used for system-maintained materialized query tables, cannot be invoked against user-maintained materialized query tables. Only a REFRESH DEFERRED materialized query table can be defined as MAINTAINED BY USER.
有啥依据吗？
MAINTAINED BY
Specifies whether the data in the materialized query table is maintained by the system, user, or replication tool. The default is SYSTEM.
SYSTEM
Specifies that the data in the materialized query table is maintained by the system.
USER
Specifies that the data in the materialized query table is maintained by the user. The user is allowed to perform update, delete, or insert operations against user-maintained materialized query tables. The REFRESH TABLE statement, used for system-maintained materialized query tables, cannot be invoked against user-maintained materialized query tables. Only a REFRESH DEFERRED materialized query table can be defined as MAINTAINED BY USER.
9同行回答
DW系统，数据是周期性的load的，那么User maintain比较好，OLTP系统，一般是不建议使用MQT的，实在是费用MQT不可，那么应是System maintain的吧收起
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上面不是说了么？你是否要对视图 insert、update 或 delete 操作，而不是对底层表进行操作来影响。。 ...ljbupc 发表于 2012-6-4 21:57
除了这个，还有别的依据吗？由系统维护的。当创建这种类型的 MQT 时，可以指定表数据是 REFRESH IMMEDIATE 还是 REFRESH DEFERRED。通过 REFRESH 关键字可以指定如何维护数据。DEFERRED 的意思是，表中的数据可以在任何时候通过 REFRESH TABLE 语句来刷新。不管是 REFRESH DEFERRED 还是 REFRESH IMMEDIATE 类型的系统维护的 MQT，对它们的 insert、update 或 delete 操作都是不允许的。但是，对于 REFRESH IMMEDIATE 类型的系统维护的 MQT，可以通过 对底层表的更改（即 insert、update 或 delete 操作）来更新。
由用户维护的。只有 REFRESH DEFERRED 物化查询表可以定义为 MAINTAINED BY USER。不能对用户维护的 MQT 发出 REFRESH TABLE 语句（用于系统维护的 MQT）。但是，用户维护的 MQT 却 允许对它们执行 insert、update 或 delete 操作。
具体可参考：http://www.ibm.com/developerwork ... les/dm-0509melnyk/#收起
由用户维护的。只有 REFRESH DEFERRED 物化查询表可以定义为 MAINTAINED BY USER。不能对用户维护的 MQT 发出 REFRESH TABLE 语句（用于系统维护的 MQT）。但是，用户维护的 MQT 却 允许对它们执行 insert、update 或 delete 操作。
具体可参考：http://www.ibm.com/developerwork ... les/dm-0509melnyk/#收起
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刷新mqt时如果需要手动维护一般用by user，自动用by system. 实际中大多在用by user收起
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