hive or impala function to get substring of a string - hive

Question

My string(its a hive query) is having many FROM and JOIN statements and i want to use Regex function to get all the sub-strings after these statements.
Below is the sample string:
str=
'select col1, col2, col3 from dbname.table1,table2
left JOIN table3
on id=id
cross JOIN table4
where filter='check'
AND row<1
AND id=5'
Required output should be:
Ex:
select Regex(str,'from ') => dbname.table1,table2
select Regex(str,'JOIN ') => table3 table4

Answer 1

You can use the following regular expression to capture the tables followed by FROM or JOIN keyword.
((JOIN|join|From|from)\s)\w+((\.|,)\w+){0,}
Note that I have used keywords in simple and capital format. You can use only one format if the query string is consistent with the regex or you can do a case insensitive match.
The above regex will give the following result.
Case 1 : From
Full Match: from dbname.table1,table2
Match Group1: from (note the space at the end)
Case 2 : Join
Full Match: JOIN table3 and JOIN table4
Match Group1: JOIN (note the space at the end)
On every match, now you can use match group1 result to replace the unwanted prefix (from or JOIN ) from the full match result to get the table names.
Use this site to play and learn regex: https://regex101.com/
EDIT 1
In hive
regexp_extract('fooblabar', 'foo(.*?)(bar)', 1)
will give you the first group. In this case, it's bla
EDIT 2
Small update on the regular expression to capture the result in group3
((JOIN|join|From|from)\s)(\w+((\.|,)\w+){0,})
This should do the trick
select split(trim(regexp_replace('select Id from test1 where join test2','((JOIN|join|From|from)\s)(\w+((\.|,)\w+){0,})',' $3')),' ');