Please explain sql statement

Category: Web Develop
 
apache_21cn
2012-05-27 04:55:51

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db2 database table Category
a structure
cat_id
name
par_cat_id
have a piece of code:
with RectCatList (cat_id, name) as
selectv root.cat_id, root.name
from Category root
where root.cat_id = null
union all
select child.cat_id child.name
from RectCatList parent, Category child
where parent.cat_id = child.par_cat_id
)
select cat_id, name from RectCatList

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