Answers for "different between inner join and outer join"

join vs inner join

-- Rows with ID existing in both a and b
-- JOIN is equivalent to INNER JOIN
SELECT a.ID, a.NAME, b.VALUE1 FROM table1 a 
  JOIN table2 b ON a.ID = b.ID
WHERE a.ID >= 1000;
-- ⇓ Test it ⇓ (Fiddle source link)

difference between inner join vs outer join

INNER JOIN:
is used when retrieving data from multiple
tables and will return only matching data.

LEFT OUTER JOIN:
is used when retrieving data from
multiple tables and will return
left table and any matching right table records.

RIGHT OUTER JOIN:
is used when retrieving data from
multiple tables and will return right
table and any matching left table records

FULL OUTER JOIN:
is used when retrieving data from
multiple tables and will return both
table records, matching and non-matching.