Duplicate data from table | not Duplicate data from table

1. select state_prefix from samplezip  group by state_prefix


2. Duplicate data from table

select count(city),city from samplezip group by city having(count(city)>1)

3. Not Duplicate Data

select count(city),city from samplezip group by city having(count(city)=1)




Here's a handy query for finding duplicates in a table. Suppose you want to find all email addresses in a table that exist more than once:

SELECT email,
 COUNT(email) AS NumOccurrences
FROM users
GROUP BY email
HAVING ( COUNT(email) > 1 )

You could also use this technique to find rows that occur exactly once:

SELECT email
FROM users
GROUP BY email
HAVING ( COUNT(email) = 1 )