A hierarchy is built upon a parent-child relationship within the same table or view.
is one of the very first features of the Oracle Database. In a traditional query, Oracle looks for a good execution plan and retrieves the rows one after the other, in no specific order.
In a hierarchy, the rows are organized as a tree, and I do not mean oak tree, I mean binary tree.
SYS_CONNECT_BY_PATH (column, char)
DESCRIPTION SYS_CONNECT_BY_PATH is valid only in hierarchical queries. It returns the path of a column value from root to node, with column values separated by char for each row returned by the CONNECT BY condition.