MySQL method for deleting duplicate record statements

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 primary key
Ask for such a result
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 a
From Table a LEFT join (
Select (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, look for redundant records in the table, duplicate records are based on a single field (Peopleid) to determine
SELECT * from People
where Peopleid in (select Peopleid from People GROUP by Peopleid have count (Peopleid) > 1)
2, delete redundant records in the table, duplicate records are based on a single field (Peopleid) to judge, leaving only the smallest ROWID records
Delete from people
where Peopleid in (select Peopleid from People GROUP by Peopleid have count (Peopleid) > 1)
and rowID not in (select min (rowid) from people GROUP by Peopleid have Count (Peopleid) >1)
3. Find redundant duplicate records (multiple fields) in the table
SELECT * FROM Vitae a
where (A.PEOPLEID,A.SEQ) in (select Peopleid,seq from Vitae GROUP by PEOPLEID,SEQ have count (*) > 1)
4. Delete extra duplicate records (multiple fields) in the table, leaving only the record with ROWID minimum
Delete from Vitae a
where (A.PEOPLEID,A.SEQ) in (select Peopleid,seq from Vitae GROUP by PEOPLEID,SEQ have count (*) > 1)
and rowID not in (select min (rowid) from Vitae GROUP by PEOPLEID,SEQ have Count (*) >1)
5. Find redundant duplicate records (multiple fields) in the table, not including the smallest ROWID records
SELECT * FROM Vitae a
where (A.PEOPLEID,A.SEQ) in (select Peopleid,seq from Vitae GROUP by PEOPLEID,SEQ have count (*) > 1)
and rowID not in (select min (rowid) from Vitae GROUP by PEOPLEID,SEQ have Count (*) >1)
Two
Say
A field "name" exists in table A,
and the "name" value may be the same between different records,
Now is the need to query out the records in the table, "name" value has duplicate entries;
Select Name,count (*) from A Group by Name have Count (*) > 1
If you also look at the same gender, the following is true:
Select Name,sex,count (*) from A Group by Name,sex have Count (*) > 1
Three
Method One
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 main field = @id
Fetch cur_rows into @id, @max
End
Close Cur_rows
Set ROWCOUNT 0 Method two
Duplicate records have two meanings of duplicate records, one is a completely duplicate record, that is, all fields are duplicated records, second, some key fields duplicate records, such as the Name field is repeated, and the other fields may not be repeated or repeated can be ignored.
1, for the first kind of repetition, easier to solve, using
SELECT DISTINCT * from TableName
You can get a result set with no duplicate records.
If the table needs to delete duplicate records (duplicate records retain 1), you can delete them as follows
SELECT DISTINCT * to #Tmp from TableName
drop table TableName
SELECT * Into TableName from #Tmp
drop table #Tmp
This duplication occurs because the table is poorly designed and the unique index columns are added to resolve.
2, this kind of repetition problem usually requires to keep the first record in the duplicate record, the operation method is as follows
Suppose there is a duplicate field name,address, which requires the result set to be unique 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 on (select Autoid from #tmp2)
The last select is the result set that name,address not duplicate (but one more autoid field, which can be written in the SELECT clause without this column in the actual write)
Four
Duplicate query
SELECT * FROM tablename where ID in (
Select ID from tablename
GROUP BY ID
Having count (ID) > 1
)
I've been learning SQL for a while and found that there were a lot of duplicate records in the table I built for testing (without indexing). Some methods for deleting duplicate records are summarized later, in Oracle, you can delete duplicate records through a unique ROWID implementation, or you can create a temporary table to implement ... This only refers to a few of the simple and practical methods, hoping to share with you (for example, table employee).
Sql> DESC Employee
Name Null? Type
----------------------------------------- -------- ------------------
emp_id Number (10)
Emp_name VARCHAR2 (20)
Salary Number (10,2)
You can query for duplicate records by using the following statement:
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 the employee GROUP by Emp_id,emp_name,salary have 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. Removal of several methods:
(1) Through the establishment of temporary tables to achieve
Sql>create table Temp_emp as (SELECT DISTINCT * from employee)
Sql> TRUNCATE TABLE employee; (Clears data from employee table)
sql> INSERT INTO employee select * from Temp_emp; (The contents of the temporary table are then inserted back)
(2) Delete duplicate records with unique ROWID implementation. In Oracle, each record has a single rowid,rowid that is unique throughout the database, and ROWID determines which data file, block, and line is in Oracle for each record. In duplicate records, the contents of all columns may be the same, but the ROWID will not be the same, so just make sure that the duplicate records have the largest or smallest rowid, and all the rest is deleted.
Sql>delete from employee E2 where rowID not in (
Select Max (E1.ROWID) from employee E1 where
e1.emp_id=e2.emp_id and E1.emp_name=e2.emp_name and e1.salary=e2.salary);--it is also possible to use min (ROWID) here.
Sql>delete from employee E2 where rowID < (
Select Max (E1.ROWID) from employee E1 where
E1.EMP_ID=E2.EMP_ID and E1.emp_name=e2.emp_name and
E1.salary=e2.salary);
(3) also through ROWID, but more efficient.
Sql>delete from employee where rowID not in (
Select Max (T1.ROWID) from the employee T1 GROUP by
T1.emp_id,t1.emp_name,t1.salary);--it is also possible to use min (ROWID) here.
emp_id Emp_name SALARY
---------- ---------------------------------------- ----------
1 Sunshine 10000
3 xyz 30000
2 Semon 20000
Sql> DESC Employee
Name Null? Type
----------------------------------------- -------- ------------------
emp_id Number (10)
Emp_name VARCHAR2 (20)
Salary Number (10,2)
You can query for duplicate records by using the following statement:
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 the employee GROUP by Emp_id,emp_name,salary have 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. Removal of several methods:
(1) Through the establishment of temporary tables to achieve
Sql>create table Temp_emp as (SELECT DISTINCT * from employee)
Sql> TRUNCATE TABLE employee; (Clears data from employee table)
sql> INSERT INTO employee select * from Temp_emp; (The contents of the temporary table are then inserted back)
(2) Delete duplicate records with unique ROWID implementation. In Oracle, each record has a single rowid,rowid that is unique throughout the database, and ROWID determines which data file, block, and line is in Oracle for each record. In duplicate records, the contents of all columns may be the same, but the ROWID will not be the same, so just make sure that the duplicate records have the largest or smallest rowid, and all the rest is deleted.
Sql>delete from employee E2 where rowID not in (
Select Max (E1.ROWID) from employee E1 where
e1.emp_id=e2.emp_id and E1.emp_name=e2.emp_name and e1.salary=e2.salary);--it is also possible to use min (ROWID) here.
Sql>delete from employee E2 where rowID < (
Select Max (E1.ROWID) from employee E1 where
E1.EMP_ID=E2.EMP_ID and E1.emp_name=e2.emp_name and
E1.salary=e2.salary);
(3) also through ROWID, but more efficient.
Sql>delete from employee where rowID not in (
Select Max (T1.ROWID) from the employee T1 GROUP by
T1.emp_id,t1.emp_name,t1.salary);--it is also possible to use min (ROWID) here.
emp_id Emp_name SALARY
---------- ---------------------------------------- ----------
1 Sunshine 10000
3 xyz 30000
2 Semon 20000

MySQL method for deleting duplicate record statements