INSERT

Basic INSERT

Let’s say we have a simple table called person:

CREATE TABLE person (
    person_id BIGINT,
    name VARCHAR(255).
    age INT,
    city VARCHAR(255)
);

The most basic insert involves inserting all values in the table:

INSERT INTO person VALUES (1, 'john doe', 25, 'new york');

If you want to insert only specific columns, you need to explicitly indicate which columns:

INSERT INTO person (name, age) VALUES ('john doe', 25);

Note that if any constraints exist on the table , such as NOT NULL, you will be required to include those columns in either case.

Inserting multiple rows

You can insert multiple rows in the database at the same time:

INSERT INTO person (name, age) VALUES 
  ('john doe', 25),
  ('jane doe', 20);

Insert from select

You can insert data in a table as the result of a select statement:

INSERT INTO person SELECT * FROM tmp_person WHERE age < 30;

Note that the projection of the select must match the columns required for the insert. In this case, the tmp_person table has the same columns as person.

Insert data using COPY

COPY is PostgreSQL’s bulk-insert mechanism. It’s a convenient way to transfer data between files and tables, but it’s also far faster than INSERT when adding more than a few thousand rows at a time.

Let’s begin by creating sample data file.

cat > samplet_data.csv

1,Yogesh
2,Raunak
3,Varun
4,Kamal
5,Hari
6,Amit

And we need a two column table into which this data can be imported into.

CREATE TABLE copy_test(id int, name varchar(8));

Now the actual copy operation, this will create six records in the table.

COPY copy_test FROM '/path/to/file/sample_data.csv' DELIMITER ',';

Instead of using a file on disk, can insert data from stdin

COPY copy_test FROM stdin DELIMITER ',';
Enter data to be copied followed by a newline.
End with a backslash and a period on a line by itself.
>> 7,Amol
>> 8,Amar
>> \.
Time: 85254.306 ms

SELECT * FROM copy_test ;
 id |  name
----+--------
  1 | Yogesh
  3 | Varun
  5 | Hari
  7 | Amol
  2 | Raunak
  4 | Kamal
  6 | Amit
  8 | Amar

Also you can copy data from a table to file as below:

COPY copy_test TO 'path/to/file/sample_data.csv'  DELIMITER ',';

For more details on COPY you can check here

INSERT data and RETURING values

If you are inserting data into a table with an auto increment column and if you want to get the value of the auto increment column.

Say you have a table called my_table:

CREATE TABLE my_table
(
id serial NOT NULL, -- serial data type is auto incrementing four-byte integer
name character varying,
contact_number integer,
CONSTRAINT my_table_pkey PRIMARY KEY (id)
);

If you want to insert data into my_table and get the id of that row:

INSERT INTO my_table(name, contact_number) VALUES ( 'USER', 8542621) RETURNING id;

Above query will return the id of the row where the new record was inserted.

SELECT data into file.

You can COPY table and paste it into a file.

postgres=# select * from my_table;
 c1 | c2 | c3 
----+----+----
  1 |  1 |  1
  2 |  2 |  2
  3 |  3 |  3
  4 |  4 |  4
  5 |  5 |   
(5 rows)

postgres=# copy my_table to '/home/postgres/my_table.txt' using delimiters '|' with null as 'null_string' csv header;
COPY 5
postgres=# \! cat my_table.txt
c1|c2|c3
1|1|1
2|2|2
3|3|3
4|4|4
5|5|null_string

UPSERT - INSERT … ON CONFLICT DO UPDATE…

since version 9.5 postgres offers UPSERT functionality with INSERT statement.

Say you have a table called my_table, created in several previous examples. We insert a row, returning PK value of inserted row:

b=# INSERT INTO my_table (name,contact_number) values ('one',333) RETURNING id;
 id
----
  2
(1 row)

INSERT 0 1

Now if we try to insert row with existing unique key it will raise an exception:

b=# INSERT INTO my_table values (2,'one',333);
ERROR:  duplicate key value violates unique constraint "my_table_pkey"
DETAIL:  Key (id)=(2) already exists.

Upsert functionality offers ability to insert it anyway, solving the conflict:

b=# INSERT INTO my_table values (2,'one',333) ON CONFLICT (id) DO UPDATE SET name = my_table.name||' changed to: "two" at '||now() returning *;
 id |                       name                             | contact_number
----+-----------------------------------------------------------------------------------------------------------+----------------
  2 | one changed to: "two" at 2016-11-23 08:32:17.105179+00 |            333
(1 row)

INSERT 0 1