Databases: deduplication and querying duplicate data

Source: Internet
Author: User

In a database table, duplicate values may be included. That's not a problem, but sometimes you might want to just list different values (distinct). Keyword DISTINCT is used to return only different values.

Table A:

1. Acting on a single row
Select distinct  from A

The following results are performed:

Acting on multi-column Example 2.1
Select distinct  from A
The following results are performed:

In fact, it is the same way that access and SQL Server support it, depending on the name and ID two fields.

There are times when you need to query for records of duplicate data, which you can summarize with GROUP by:

Select ID  from A
Group by having Count (1>=2

Databases: deduplication and querying duplicate data

Contact Us

The content source of this page is from Internet, which doesn't represent Alibaba Cloud's opinion; products and services mentioned on that page don't have any relationship with Alibaba Cloud. If the content of the page makes you feel confusing, please write us an email, we will handle the problem within 5 days after receiving your email.

If you find any instances of plagiarism from the community, please send an email to: info-contact@alibabacloud.com and provide relevant evidence. A staff member will contact you within 5 working days.

A Free Trial That Lets You Build Big!

Start building with 50+ products and up to 12 months usage for Elastic Compute Service

  • Sales Support

    1 on 1 presale consultation

  • After-Sales Support

    24/7 Technical Support 6 Free Tickets per Quarter Faster Response

  • Alibaba Cloud offers highly flexible support services tailored to meet your exact needs.