Mysql Delete Duplicate Record statement method _mysql

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 statements for querying and deleting duplicate records
SQL statements for querying and deleting duplicate records
1, look for redundant records in the table, duplicate records are based on a single field (Peopleid) to judge
SELECT * from People
where Peopleid in (select Peopleid from People GROUP by Peopleid has count (Peopleid) > 1)
2, delete redundant records in the table, duplicate records are based on a single field (Peopleid) to judge, leaving only rowid minimal records
Delete from people
where Peopleid in (select Peopleid from People GROUP by Peopleid has count (Peopleid) > 1)
and rowID not in (select min (rowid) from people GROUP by Peopleid have Count (Peopleid) >1)
3. Find redundant records in the table (multiple fields)
SELECT * FROM Vitae a
where (A.PEOPLEID,A.SEQ) in (select Peopleid,seq from Vitae GROUP by PEOPLEID,SEQ have count (*) > 1)
4, delete redundant records in the table (multiple fields), leaving only the smallest ROWID records
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, look for redundant records in the table (multiple fields), does not contain 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
There is a field "name" in Table A,
and the "name" value may be the same between different records,
Now you need to query the records in the table, the "name" value duplicates the item;
Select Name,count (*) from-A Group by Name has Count (*) > 1
If the same gender is also the same large as the following:
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 record" has two duplicate records, one is a completely duplicate record, that is, all the fields are duplicate records, the second is a part of 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)
Four
Query duplication
SELECT * FROM tablename where ID in (
Select ID from tablename
GROUP BY ID
Having count (ID) > 1
)
After learning about SQL for a while, I found a lot of duplicate records in the table I built to test (not indexed). Later, we summarize some ways to delete duplicate records, in Oracle, you can delete duplicate records through the unique ROWID, and you can build temporary tables to implement ... This only refers to a few of the simple and practical methods, I hope to share with you (take 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 query for duplicate records through 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 Employee GROUP BY Emp_id,emp_name,salary has 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. Several methods of deletion:
(1) By establishing a temporary table to achieve
Sql>create table Temp_emp as (SELECT DISTINCT * from employee)
Sql> TRUNCATE TABLE employee; (Empty the Employee table data)
Sql> INSERT INTO the employee select * from Temp_emp; (and insert the contents of the temporary table back)
(2) Delete duplicate records through a unique ROWID implementation. In Oracle, each record has a rowid,rowid that is unique across the database, ROWID determines which data files, blocks, and rows are in Oracle for each record. In a duplicate record, all columns may have the same content, but ROWID will not be the same, so just make sure that those with the largest or smallest rowid in the duplicate record are OK, and all the rest is deleted.
Sql>delete from employee E2 where ROWID isn't 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)--This is also possible with min (ROWID).
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 the efficiency is higher.
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);--This is also possible with min (ROWID).
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 through 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 Employee GROUP BY Emp_id,emp_name,salary has 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. Several methods of deletion:
(1) By establishing a temporary table to achieve
Sql>create table Temp_emp as (SELECT DISTINCT * from employee)
Sql> TRUNCATE TABLE employee; (Empty the Employee table data)
Sql> INSERT INTO the employee select * from Temp_emp; (and insert the contents of the temporary table back)
(2) Delete duplicate records through a unique ROWID implementation. In Oracle, each record has a rowid,rowid that is unique across the database, ROWID determines which data files, blocks, and rows are in Oracle for each record. In a duplicate record, all columns may have the same content, but ROWID will not be the same, so just make sure that those with the largest or smallest rowid in the duplicate record are OK, and all the rest is deleted.
Sql>delete from employee E2 where ROWID isn't 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)--This is also possible with min (ROWID).
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 the efficiency is higher.
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);--This is also possible with min (ROWID).
emp_id Emp_name SALARY
---------- ---------------------------------------- ----------
1 Sunshine 10000
3 xyz 30000
2 Semon 20000