Insert data in 3 tables at a time using Postgres

Question

I want to insert data into 3 tables with a single query.
My tables looks like below:

CREATE TABLE sample (    id        bigserial PRIMARY KEY,    lastname  varchar(20),    firstname varchar(20) );  CREATE TABLE sample1(    user_id    bigserial PRIMARY KEY,    sample_id  bigint REFERENCES sample,    adddetails varchar(20) );  CREATE TABLE sample2(    id      bigserial PRIMARY KEY,    user_id bigint REFERENCES sample1,    value   varchar(10) ); 

I will get a key in return for every insertion and I need to insert that key in the next table.
My query is:

insert into sample(firstname,lastname) values('fai55','shaggk') RETURNING id; insert into sample1(sample_id, adddetails) values($id,'ss') RETURNING user_id; insert into sample2(user_id, value) values($id,'ss') RETURNING id; 

But if I run single queries they just return values to me and I cannot reuse them in the next query immediately.

How to achieve this?

Answer 1

Use data-modifying CTEs:

WITH ins1 AS (    INSERT INTO sample(firstname, lastname)    VALUES ('fai55', 'shaggk') -- ON     CONFLICT DO NOTHING         -- optional addition in Postgres 9.5+    RETURNING id AS sample_id    ) , ins2 AS (    INSERT INTO sample1 (sample_id, adddetails)    SELECT sample_id, 'ss' FROM ins1    RETURNING user_id    ) INSERT INTO sample2 (user_id, value) SELECT user_id, 'ss2' FROM ins2; 

Each INSERT depends on the one before. SELECT instead of VALUES makes sure nothing is inserted in subsidiary tables if no row is returned from a previous INSERT. (Since Postgres 9.5+ you might add an ON CONFLICT.)
It's also a bit shorter and faster this way.

Typically, it's more convenient to provide complete data rows in one place:

WITH data(firstname, lastname, adddetails, value) AS (    VALUES                              -- provide data here       ('fai55', 'shaggk', 'ss', 'ss2') -- see below     , ('fai56', 'XXaggk', 'xx', 'xx2') -- works for multiple input rows        --  more?                          ) , ins1 AS (    INSERT INTO sample (firstname, lastname)    SELECT firstname, lastname          -- DISTINCT? see below    FROM   data    -- ON     CONFLICT DO NOTHING       -- UNIQUE constraint? see below    RETURNING firstname, lastname, id AS sample_id    ) , ins2 AS (    INSERT INTO sample1 (sample_id, adddetails)    SELECT ins1.sample_id, d.adddetails    FROM   data d    JOIN   ins1 USING (firstname, lastname)    RETURNING sample_id, user_id    ) INSERT INTO sample2 (user_id, value) SELECT ins2.user_id, d.value FROM   data d JOIN   ins1 USING (firstname, lastname) JOIN   ins2 USING (sample_id); 

db<>fiddle here

You may need explicit type casts in a stand-alone VALUES expression - as opposed to a VALUES expression attached to an INSERT where data types are derived from the target table. See:

• Casting NULL type when updating multiple rows

If multiple rows can come with identical (firstname, lastname), you may need to fold duplicates for the first INSERT:

... INSERT INTO sample (firstname, lastname) SELECT DISTINCT firstname, lastname FROM data ... 

You could use a (temporary) table as data source instead of the CTE data.

It would probably make sense to combine this with a UNIQUE constraint on (firstname, lastname) in the table and an ON CONFLICT clause in the query.

Related:

• How to use RETURNING with ON CONFLICT in PostgreSQL?
• Is SELECT or INSERT in a function prone to race conditions?