server| Repeat | Repeat the following to illustrate the issue of duplicate record deletion.
There are two duplicates of the record, one is a completely duplicate record, that is, all the fields are duplicate records, the second is some key fields duplicate records, such as the Name field repeat, and other fields do not necessarily repeat or repeat can be ignored.
1, for the first repetition, easier to solve, the use of
SELECT DISTINCT * FROM tablename
You can get a result set without duplicate records.
If the table needs to delete duplicate records (1 of duplicate records are retained), you can delete them in the following ways
SELECT DISTINCT * into #Tmp tablename
DROP TABLE TableName
SELECT * INTO TableName from #Tmp
drop table #Tmp
This duplication occurs because the table is poorly designed and can be resolved by adding a unique index column.
2. This type of repetition usually requires the first record in the duplicate record to be retained, as follows
Suppose there is a duplicate field of name,address that requires a unique result set for both 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 gets the name,address result set (but one more autoid field, which can be written in the SELECT clause to omit this column)
