Filter duplicate data

Select * from zxzx t where id in (select max (id) from zxzx t1 group by t1.type) order by id desc

The above example is filtered by type.

The following is an excerpt from the Internet:

I. Filtering duplicate data

1. Completely Repeated Records

/* Function: the specified field is completely repeated */
Select distinct field 1, Field 2, Field 3 from data table
2. Record with duplicate key fields

/* Data Structure: Role file (role encoding, role, and role classification encoding)
Function: retrieves the unique data with the specified field (role classification encoding) as the keyword.
Description: repeat the record to get the last one. You only need to change min to max.
*/
Select * from role file t where role code in (select min (role code) from role file t1 group by t1. role classification code)
Ii. Delete duplicate records

During database usage, due to program problems, duplicate data may occur, leading to incorrect database settings. This example describes how to delete the data.

Method 1:

Declare @ max integer, @ id integer
Declare cur_rows cursor local for select Main field, count (*) from table name group by main field having count (*)> 1
Open cur_rows
Fetch cur_rows into @ id, @ max
While @ fetch_status = 0
Begin
Select @ max = @ max-1
Set rowcount @ max
Delete from table name where primary field = @ id
Fetch cur_rows into @ id, @ max
End
Close cur_rows
Set rowcount 0
Method 2:

There are two Repeated Records. One is a completely repeated record, that is, records with all fields being repeated, and the other is records with duplicate key fields, such as duplicate Name fields, other fields are not necessarily repeated or can be ignored.

1. For the first type of repetition, it is easier to solve.

Select distinct * from tableName
You can get the result set without repeated records.

If the table needs to delete duplicate records (one record is retained), you can delete the record as follows:

Select distinct * into # Tmp from tableName
Drop table tableName
Select * into tableName from # Tmp
Drop table # Tmp
The reason for this repetition is that the table design is not weekly. You can add a unique index column.

2. Repeat problems usually require that the first record in the repeat record be retained. The procedure is as follows:

Assume that the duplicate fields are Name and Address. You must obtain the unique result set of the two fields.

Select identity (int, 1, 1) as autoID, * into # Tmp from tableName
Select min (autoID) as autoID into # Tmp2 from # Tmp group by Name, autoID
Select * from # Tmp where autoID in (select autoID from # tmp2)
The last select command gets the result set with no duplicate Name and Address (but an autoID field is added, which can be omitted in the select clause when writing ). Original article: http://www.chinaitpower.com/2006Aug/2006-08-23/212751.html