Several Methods for deleting duplicate data in a database

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 repeat, it is easy to solve. You can use select distinct * from tableName to obtain 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)