DB2 数据库的快照和视图获取方法
一直以为空字符串是就是NULL，当插入空字符串的时候就可以通过NULL，但是前段时间开发发现使用not in特定值后发现，空字符集居然
今天在工作中，同事提到如何获取表中的LOB占用空间大小，通常我们常用syscat.tables查询表中的fpages和npages等信息，但是这个未将将普通字段和LOB字段分开的，有同事就采用get snapshot方式获取了表的快照信息，确实能够很清楚的看到表中数据信息，将LOB和普通字段页数分开显示。
其实查查看对于获取表的类似信息的可供查询的方法还是很多：
1.表函数admin_get_tab_info,不过该表函数将要被后面要提到的管理视图替代，慢慢就被抛弃的功能，
用法类似SELECT * FROM TABLE (SYSPROC.ADMIN_GET_TAB_INFO('DBUSER1','EMPLOYEE')) AS T
2.表函数snap_get_tab,这也是一个即将被抛弃的功能，主要是之前的DB2的健康快照工具在新的版本中已经没了，尤其是10.1，已经不再有DB2控制中心这个管理工具了，所以相关API接口也就会关闭掉。
SELECT * FROM TABLE (SYSPROC.ADMIN_GET_TAB_INFO('SAMPLE',0)) AS T，当然，这个会查询整库的表的信息。
3.查询sysibmadm.snaptab快照视图，这个是迄今为止，DB2开始大力推进的供用户方便查询的管理视图
4.表函数snap_get_tab_v91返回和3中相同的快照信息
看来DB2真的是越来越接近用户使用习惯了，其实管理视图方式很好用的，日常基本通过其查询，就不用通过实例快照方式获取想要的信息，真的很方便，很好很强大的吧。
DB2数据库性能调整和优化(第1、2版) PDF
DB2数据库性能优化介绍
DB2 9.7 for Linux 5.4安装详细步骤
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