SQL基础-->层次化查询(START BY ... CONNECT BY PRIOR)
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层次化查询,即树型结构查询,是SQL中经常用到的功能之一,通常由根节点,父节点,子节点,叶节点组成,其语法如下:
SELECT [LEVEL] ,column,expression,...
FROM table_name
[WHERE where_clause]
[[START WITH start_condition] [CONN......
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