connect by clause in regex_substr

Question

I cant get the understanding of this statement - not eveN after googling around

 
pv_no_list :=\'23,34,45,56\';
SELECT   DISTINCT REGEXP_SUBSTR (pv_no_li         


        

Answer 1

connect by has nothing to do with regex_substr:

• The first is to perform a hierarchical query, see http://docs.oracle.com/cd/B19306_01/server.102/b14200/queries003.htm

• The second is to get a substring using regular expressions.

This query "abuses" the connect by functionality to generate rows in a query on dual. As long as the expression passed to connect by is true, it will generate a new row and increase the value of the pseudo column LEVEL.

Then LEVEL is passed to regex_substr to get the nth value when applying the regular expression.