Question

Table:

ProductComapny

Fields:id,name

ProductComapny content 10000 recorde.

now i want id set primary key But a number of id recordings have been repeated

1.how can id set primary key???

2.how can remove duplicate recorde?

3.How can I get the number of duplicate records?

BY SQL In SqlServer And MySql

For Study

Answer 1

Answered for SQL Server – This won’t work in MySQL. Please specify which, rather than patronising people who are able to help you.

To get the count of duplicates:

SELECT id, name, COUNT(*) FROM productCompany GROUP BY id, name

To apply a primary key, first delete the duplicates as follows:

WITH sorted AS
(
  SELECT
    ROW_NUMBER() OVER (PARTITION BY id, name) AS duplicate_id,
    id,
    name
  FROM
    productCompany
)
DELETE
  sorted
WHERE
  duplicate_id > 1

Then use Management Studio to apply your primary key.