How Can I Sequentially Insert Data into Multiple Postgres Tables Using CTEs or a Temporary Table?

Using Postgres CTE to sequentially insert data in multiple tables

In Postgres, you can use data modifying common table expressions (CTE) to insert data into multiple tables with a single query. CTE provides a convenient way to define temporary result sets and manipulate data in a single query.

Use data to modify CTE

The following query demonstrates how to use CTE to sequentially insert data into three tables:

<code class="language-sql">WITH ins1 AS (
   INSERT INTO sample(firstname, lastname)
   VALUES ('fai55', 'shaggk')
   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;</code>

In this query:

• The first CTE, ins1, inserts a row into the sample table and returns the ID of the inserted row as sample_id.
• The second CTE, ins2, uses the ins1 returned by sample_id to insert a row into the sample1 table. It returns the user_id of the inserted row.
• The final INSERT statement inserts a row into the ins2 table using the user_id returned by sample2.

This approach allows you to chain multiple INSERT statements and reuse values ​​returned from previous inserts.

Handling concurrent writes

If multiple sessions are inserting data at the same time, you must consider the possibility of concurrent writes. To do this, you can use the ON CONFLICT clause to specify the behavior when trying to insert a duplicate record.

Alternatives using temporary tables

As an alternative to using CTE, you can also create a temporary table to hold the intermediate data and then perform the inserts sequentially:

<code class="language-sql">CREATE TEMP TABLE tmp AS SELECT * FROM sample;
INSERT INTO sample1 (sample_id, adddetails) SELECT id, 'ss' FROM tmp;
INSERT INTO sample2 (user_id, value) SELECT user_id, 'ss2' FROM tmp;
DROP TABLE tmp;</code>

This approach involves using a temporary table as the data source for subsequent inserts without directly linking the CTE.

By using a data modification CTE or temporary table, you can efficiently insert data into multiple tables with a single Postgres query, thus simplifying data insertion operations.

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