Frequent tables to store tree structures such as unit organization
Two words in the SELECT statement
Connect by Prior Conditions
START WITH condition
Connect By is a connection to the "zipper", and the prior represents the execution of the parent child relationship query start with where to start from top, from the bottom
In the table of the tree structure, each tuple can have a layer number (Level), a more node is 1
Available system variables LEVEL
SELECCCT Level. . . Connect by. . .
Branch query:
