PostgreSQL deletes duplicate data

PostgreSQL usually finds one of the duplicate data and removes other duplicate values with a unique condition. Oracle deduplication is implemented in many ways. It is commonly used to perform deduplication Based on rowid. How does the PostgreSQL database remove duplicate data from a single table? You can use ctid. The following is the experiment process. 1. Create a test table david

PostgreSQL usually finds one of the duplicate data and removes other duplicate values with a unique condition. Oracle deduplication is implemented in many ways. It is commonly used to perform deduplication Based on rowid. How does the PostgreSQL database remove duplicate data from a single table? You can use ctid. The following is the experiment process. 1. Create a test table david

PostgreSQL deletes duplicate data

Deduplication is generally used to locate one of the duplicate data and remove other duplicate values with a unique condition.

Oracle deduplication is implemented in many ways. It is commonly used to perform deduplication Based on rowid.

How does the PostgreSQL database remove duplicate data from a single table? You can use ctid. The following is the experiment process.

I. Create a test table

David = # create table emp (

David (# id int,

David (# name varchar );

CREATE TABLE

David = #

2. Insert Test Data

David = # insert into emp values (1, 'David ');

INSERT 0 1

David = # insert into emp values (1, 'David ');

INSERT 0 1

David = # insert into emp values (1, 'David ');

INSERT 0 1

David = # insert into emp values (2, 'sandy ');

INSERT 0 1

David = # insert into emp values (2, 'sandy ');

INSERT 0 1

David = # insert into emp values (3, 'renee ');

INSERT 0 1

David = # insert into emp values (4, 'jack ');

INSERT 0 1

David = # insert into emp values (5, 'Rose ');

INSERT 0 1

David = #

Iii. query initialization data

David = # select ctid, * from emp;

Ctid | id | name

------- + ---- + -------

(0, 1) | 1 | david

(0, 2) | 1 | david

(0, 3) | 1 | david

(0, 4) | 2 | sandy

(0, 5) | 2 | sandy

(0, 6) | 3 | renee

(0, 7) | 4 | jack

(0, 8) | 5 | rose

(8 rows)

David = #

Query repeated data count

David = # select distinct id, count (*) from emp group by id having count (*)> 1;

Id | count

---- + -------

1 | 3

2 | 2

(2 rows)

David = #

Three records with id 1 and two records with id 2 are found.

4. query the data to be retained

Take min (ctid) or max (ctid) as the standard.

David = # select ctid, * from emp where ctid in (select min (ctid) from emp group by id );

Ctid | id | name

------- + ---- + -------

(0, 1) | 1 | david

(0, 4) | 2 | sandy

(0, 6) | 3 | renee

(0, 7) | 4 | jack

(0, 8) | 5 | rose

(5 rows)

David = #

5. Delete duplicate data

David = # delete from emp where ctid not in (select min (ctid) from emp group by id );

DELETE 3

David = #

6. view the final result

David = # select ctid, * from emp;

Ctid | id | name

------- + ---- + -------

(0, 1) | 1 | david

(0, 4) | 2 | sandy

(0, 6) | 3 | renee

(0, 7) | 4 | jack

(0, 8) | 5 | rose

(5 rows)

David = #

Note: If the table already has a unique sequence primary key value, you can replace this value with the above ctid and delete it directly.

7. Other Methods

You can also use the following SQL statement to delete duplicate data.

David = # delete from emp

David-# where a. ctid <>

David -#(

David (# select min (B. ctid) from emp B

David (# where a. id = B. id

David (#);

DELETE 3

David = #

Note: This deletion method is highly efficient when the table data volume is large.