I already a shared article on ON CONFLICT clause of PostgreSQL 9.5

PostgreSQL 9.5: Insert IF not Exists, Update IF Exists (Insert ON CONFLICT option)

In above article, I used only one single key in ON CONFLICT clause.

A day before yesterday, I got an email like, does it require to add a unique index on those columns which we require to be in ON CONFLICT clause?
The answer is: Yes

You must need to define a unique index on those columns which you are planning to use in ON CONFLICT clause because it can only check the duplicates bases on unique indexes only.

Below is a demonstration of this:

Create a table with sample data with composite PRIMARY KEY:

CREATE TABLE tbl_Employee
(	
	EmpID INT 
	,EmpName CHARACTER VARYING 
	,CONSTRAINT pk_tbl_Employee_EmpID_EmpName PRIMARY KEY (EmpID,EmpName)
);
 
INSERT INTO tbl_Employee 
VALUES (1,'Anvesh'),(2,'Roy'),(3,'Lee')
,(4,'Nivu'),(5,'Rajesh'),(6,'Nupur');

Try to insert a duplicate EmpID record, using option INSERT ON DO NOTHING:
It will insert a new record because key EmpID + EmpName is not duplicate. But if you execute the same, insert the second time, it will do nothing.

INSERT INTO tbl_Employee 
VALUES (6,'Noor')
ON CONFLICT (EmpID,EmpName)
DO NOTHING;

Check the result:

SELECT *FROM tbl_Employee;

/*
EmpID   EmpName
-----------------
1       Anvesh
2       Roy
3       Lee
4       Nivu
5       Rajesh
6       Nupur
6       Noor
*/

After a long time of waiting, PostgreSQL 9.5 introduced INSERT ON CONFLICT [DO UPDATE] [DO NOTHING].

This option basically helps to perform DML actions like, Insert IF not Exists, Update IF Exists.

Previously, we have to use upsert or merge statement to do this kind of operation. I have also published an article on it.

PostgreSQL: Insert – Update or Upsert – Merge using writable CTE

This newly option has two varieties:

• INSERT ON CONFLICT DO UPDATE: If record matched, it is updated with the new data value.
• INSERT ON CONFLICT DO NOTHING: If record matched, it skips the record or error.

Below is a full demonstration of this:

Create a table with sample data:

CREATE TABLE tbl_Employee
(	
	EmpID INT PRIMARY KEY
	,EmpName CHARACTER VARYING 
);

INSERT INTO tbl_Employee 
VALUES (1,'Anvesh'),(2,'Roy'),(3,'Lee')
,(4,'Nivu'),(5,'Rajesh'),(6,'Nupur');

Insert one more row with option INSERT ON CONFLICT DO UPDATE:

Using this option, if a conflict occurs then it will update the mentioned data.
Here, I have use “Excluded” table which is special table and contains the row-to-be-inserted.

INSERT INTO tbl_Employee 
VALUES (7,'Ramu')
ON CONFLICT (EmpID)
DO UPDATE SET EmpName = Excluded.EmpName;

INSERT INTO tbl_Employet 
VALUES (7,'Mahi')
ON CONFLICT (EmpID)
DO UPDATE SET EmpName = Excluded.EmpName;

INSERT INTO tbl_Employee 
VALUES (8,'Noor')
ON CONFLICT (EmpID)
DO NOTHING;

INSERT INTO tbl_Employee 
VALUES (8,'Noor')
ON CONFLICT (EmpID)
DO NOTHING;

SELECT *FROM tbl_Employee;

/*
EmpID   EmpName
-----------------
1       Anvesh
2       Roy
3       Lee
4       Nivu
5       Rajesh
6       Nupur
7       Mahi
8       Noor
*/