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Does select return duplicate rows?
Select Distinct will remove duplicates if the rows are actually duplicated for all columns, but will not eliminate ‘duplicates’ that have a different value in any column.
Can a table have duplicate rows?
A table contains duplicate rows when two or more rows are identical. When you create a table, you can specify the handling of duplicate rows. By default, duplicate rows are allowed. If you disallow them, an error is generated when a user attempts to insert a duplicate row into a table.
Can SQL table have duplicate rows?
According to database design best practices, a SQL Server table should not contain duplicate rows. During the database design process primary keys should be created to eliminate duplicate rows. For example, when a staging table is used and data is loaded from different sources where duplicate rows are possible.
Why does SQL allow duplicate rows?
When support for constraints (keys in particular) was later added to the language, operational systems had already been written, and nobody wanted to break backward compatibility. So it (allowing duplicates) has been there ever since.
What does it mean when there are duplicates in a table?
If any rows are returned, that means we have duplicates. In this example, our results look like this: In the previous step, our query returned a list of duplicates. Now, we want to return the entire record for each duplicate row. To accomplish this, we’ll need to select the entire table and join that to our duplicate rows.
How to return only duplicate rows in SQL?
I need to return only the rows that are exact duplicates all across the board so each record must be exctly the same as the other record for it to be a duplicate. I would like to return both records. These reocrds are mixed in with a bunch of records that do not have duplicates…
How to prevent duplicate rows in group by clause?
The GROUP BY clause at the end ensures only a single row is returned for each unique combination of columns in the GROUP BY clause. This should prevent duplicate rows being displayed in your results.
Why are there multiple tables in SQL Server?
There are multiple tables that have different information in them. Person holds the primary information about the person but not the address, or phone, or email. This is because the original designer wanted the table to be able to hold multiple phone numbers and emails and addresses.