Several Methods for SQLServer to delete duplicate records

For example, if the primary key is required to obtain such results as idnamevalue1app3biii4bpp6cpp8ciii method 1 deleteYourTablewhere [id] notin (selectmax ([id]) fromYourTablegroup

For example: id name value 1 a pp 2 a pp 3 B iii 4 B pp 5 B pp 6 c pp 7 c pp 8 c iii id is the primary key requirement to get this result id name value 1 pp 3 B iii 4 B pp 6 c pp 8 c iii method 1 delete YourTable where [id] not in (select max ([id]) from YourTable group

For example:

Id name value

1 a pp

2 a pp

3 B iii

4 B pp

5 B pp

6 c pp

7 c pp

8 c iii

Id is the primary key

This result is required.

Id name value

1 a pp

3 B iii

4 B pp

6 c pp

8 c iii

Method 1

Delete YourTable

Where [id] not in (

Select max ([id]) from YourTable

Group by (name + value ))

Method 2

Delete

From table a left join (

Select id = min (id) from Table group by name, value

) B on a. id = B. id

Where B. id is null

SQL statement for querying and deleting duplicate records

SQL statement for querying and deleting duplicate records

1. Search for redundant duplicate records in the Table. duplicate records are determined based on a single field (peopleId ).

Select * from people

Where peopleId in (select peopleId from people group by peopleId having count (peopleId)> 1)

2. Delete unnecessary duplicate records in the Table. Repeat records are determined based on a single field (eagleid), leaving only the records with the smallest rowid

Delete from people

Where peopleId in (select peopleId from people group by peopleId having count (peopleId)> 1)

And rowid not in (select min (rowid) from people group by peopleId having count (peopleId)> 1)

3. Search for redundant duplicate records in the table (multiple fields)

Select * from vitae

Where (a. peopleId, a. seq) in (select peopleId, seq from vitae group by peopleId, seq having count (*)> 1)

4. Delete redundant record (multiple fields) in the table, leaving only the records with the smallest rowid

Delete from vitae

Where (a. peopleId, a. seq) in (select peopleId, seq from vitae group by peopleId, seq having count (*)> 1)

And rowid not in (select min (rowid) from vitae group by peopleId, seq having count (*)> 1)

5. Search for redundant duplicate records (multiple fields) in the table, excluding records with the smallest rowid

Select * from vitae

Where (a. peopleId, a. seq) in (select peopleId, seq from vitae group by peopleId, seq having count (*)> 1)

And rowid not in (select min (rowid) from vitae group by peopleId, seq having count (*)> 1)

(2)

For example

There is A field "name" in Table ",

The "name" value may be the same for different records,

Now, you need to query items with duplicate "name" values between records in the table;

Select Name, Count (*) From A Group By Name Having Count (*)> 1

If the gender is also the same, the statement is as follows:

Select Name, sex, Count (*) From A Group By Name, sex Having Count (*)> 1

(3)

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

"Repeat record" has two duplicate records. One is a completely repeated record, that is, a record with all fields already exists. The other is a record with duplicate key fields, for example, the Name field is repeated, while 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)

(4)

Duplicate Query

Select * from tablename where id in (

Select id from tablename

Group by id

Having count (id)> 1

)

After learning SQL for a while, I found that many duplicate records appear in the table I created for testing (without indexing. Later I summarized some methods for deleting duplicate records. In Oracle, you can delete duplicate records by using the unique rowid. You can also create a temporary table... this article only mentions several simple and practical methods. I hope you can share them with us (using the table "employee" as an example ).

SQL> desc employee

Name Null? Type

-------------------------------------------------------------------

Emp_id NUMBER (10)

Emp_name VARCHAR2 (20)

Salary NUMBER (10, 2)

You can use the following statement to query duplicate records:

SQL> select * from employee;

EMP_ID EMP_NAME SALARY

------------------------------------------------------------

1 sunshine 10000

1 sunshine 10000

2 semon 20000

2 semon 20000

3. xyz 30000

2 semon 20000

SQL> select distinct * from employee;

EMP_ID EMP_NAME SALARY

------------------------------------------------------------

1 sunshine 10000

2 semon 20000

3. xyz 30000

SQL> select * from employee group by emp_id, emp_name, salary having count (*)> 1

EMP_ID EMP_NAME SALARY

------------------------------------------------------------

1 sunshine 10000

2 semon 20000

SQL> select * from employee e1

Where rowid in (select max (rowid) from employe e2

Where e1.emp _ id = e2.emp _ id and

E1.emp _ name = e2.emp _ name and e1.salary = e2.salary );

EMP_ID EMP_NAME SALARY

------------------------------------------------------------

1 sunshine 10000

3. xyz 30000

2 semon 20000

2. delete several methods:

(1) create a temporary table.

SQL> create table temp_emp as (select distinct * from employee)

SQL> truncate table employee; (clear the data in the employee table)

SQL> insert into employee select * from temp_emp; (insert the content in the temporary table back)