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

You could create an after insert trigger on the Sample table to insert into the other two tables.

The only issue i see with doing this is that you wont have a way of inserting adddetails it will always be empty or in this case ss. There is no way to insert a column into sample thats not actualy in the sample table so you cant send it along with the innital insert.

Another option would be to create a stored procedure to run your inserts.

You have the question taged mysql and postgressql which database are we talking about here?

Answer 2

Something like this

with first_insert as (
   insert into sample(firstname,lastname) 
   values('fai55','shaggk') 
   RETURNING id
), 
second_insert as (
  insert into sample1( id ,adddetails) 
  values
  ( (select id from first_insert), 'ss')
  RETURNING user_id
)
insert into sample2 ( id ,adddetails) 
values 
( (select user_id from first_insert), 'ss');

As the generated id from the insert into sample2 is not needed, I removed the returning clause from the last insert.

Answer 3

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.

This does not address possibly complications from concurrent writes. for that, see:

• How to use RETURNING with ON CONFLICT in PostgreSQL?

• Is SELECT or INSERT in a function prone to race conditions?

Answer 4

Typically, you'd use a transaction to avoid writing complicated queries.

http://www.postgresql.org/docs/current/static/sql-begin.html

http://dev.mysql.com/doc/refman/5.7/en/commit.html

You could also use a CTE, assuming your Postgres tag is correct. For instance:

with sample_ids as (
  insert into sample(firstname, lastname)
  values('fai55','shaggk')
  RETURNING id
), sample1_ids as (
  insert into sample1(id, adddetails)
  select id,'ss'
  from sample_ids
  RETURNING id, user_id
)
insert into sample2(id, user_id, value)
select id, user_id, 'val'
from sample1_ids
RETURNING id, user_id;