I've read that using a where exists clause could usually be more efficient than writing select distinct. How could I rewrite the below 2 queries using the where exists condition? Not sure if query2 is eligible for this clause or this only applies to joins.
Query 1:
SELECT DISTINCT
e.field1,
regexp_substr(substr(TRIM(d.field2), 1, 2), '[A-Za-z]+', 1, 1) postal_group
FROM
table1 e
JOIN table1 f ON f.field0 = e.field0
JOIN table2 g ON g.field3 = f.field3
JOIN table3 g ON g.field4 = f.field4
JOIN table4 a ON a.field5 = g.field5
JOIN table5 b ON ( b.field6 = a.field6
AND b.field7 = a.field7 )
JOIN table6 c ON ( c.field8 = b.field8
AND c.field9 = b.field9 )
JOIN table7 d ON ( d.field10 = c.field10
AND d.field11 = c.field11 )
Query 2:
SELECT DISTINCT
field
FROM
table1
WHERE
condition = 'value'