Instead of storing metadata across 18 tables, the PODS4 upload process saves it using DB2 columns of type XML and does an INSERT query into four tables.
PODS4上传过程并不在18个表中存储元数据，而是使用xml类型的DB 2列保存元数据，只需对四个表执行INSERT。
But in DB2, you must provide a value for NOT NULL columns in an INSERT statement when a default hasn't been defined.
但在DB 2中，如果未定义该值，则必须在insert语句中为NOT null列提供值。
These columns are simply hitching a ride along the INSERT operation and are accessible to the SELECT above.
这些列只是通过INSERT操作搭载的，并且上面的SELECT可以访问这些列。
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