1. use group by clause with the field on which you want to 
check for duplicates

Ex: select salary,count (*) from employee group by salary 
having count (*)>1

2. Use the below query to delete the duplicate records (not 
the original ones)

SET ROWCOUNT 1 
DELETE yourtable
FROM yourtable a
WHERE (SELECT COUNT(*) FROM yourtable b WHERE b.name1 = 
a.name1 AND b.age1 = a.age1) > 1
WHILE @@rowcount > 0
  DELETE yourtable
  FROM yourtable a
  WHERE (SELECT COUNT(*) FROM yourtable b WHERE b.name1 = 
a.name1 AND b.age1 = a.age1) > 1
SET ROWCOUNT 0

For Count Duplicate---
SELECT YourColumn, COUNT(*) TotalCount
FROM YourTable
GROUP BY YourColumn
HAVING COUNT(*) > 1
ORDER BY COUNT(*) DESC 
For delete Duplicate---
DELETE
FROM MyTable
WHERE ID NOT IN
(
SELECT MAX(ID)
FROM MyTable
GROUP BY DuplicateColumn1, DuplicateColumn2, 
DuplicateColumn2)

1. To get the duplicate records.
Use group by clause to the column on which you want to 
check the duplicates records.
syntax:
select column_name, count(*) from table_name group by 
column_name having count(*) >1

2. To delete the duplicate records.
syntax:
delete from table_name where rowid in (select max(rowid) 
from table_name group by column_name having count(*)>1 )

This will work.
Please let me know in case of any issues.