I am writing a job to transform data from an old design into a new design. In this process, I need to take the id from an insert into a separate table and use that in an insert to the target table, as such:
CREATE TABLE t1 {
t1_id BIGSERIAL,
col1 VARCHAR
};
CREATE TABLE t2 {
t2_id BIGSERIAL,
col2 VARCHAR, -- renamed from col1 to avoid confusion
t1_id BIGINT REFERENCES t1.t1_id
};
I have the SQL defined that matches the following form:
WITH ins AS (
INSERT INTO t1 (t1_id) VALUES (DEFAULT) RETURNING t1_id
) INSERT INTO t2
(col1, t1_id)
SELECT
a.val1, (SELECT * FROM ins)
FROM t3 a;
I wanted this to run the SELECT * FROM ins
for every row of the SELECT
.. but instead it only runs it once and uses that value for all rows in the SELECT
. How can I restructure my SQL to get the desired behavior?
edit4
t1 ends up looking like:
1,<NULL>
(1 row)
t2 ends up looking like:
10,'a',1
11,'b',1 -- problem with id from t1 being 1
12,'c',1 -- problem with id from t1 being 1
.
.
What I want t1 to look like:
1,<NULL>
2,<NULL>
3,<NULL>
.
.
What I want t2 to look like:
10,'a',1
11,'b',2 -- id from t1 of 2
12,'c',3 -- id from t1 of 3
.
.
edit
To address what a_horse_with_no_name said, I also tried this (with the same result):
WITH ins AS (
INSERT INTO t1 (t1_id) VALUES (DEFAULT) RETURNING t1_id
) INSERT INTO t2
(col1, t1_id)
SELECT
a.val1, b.t1_id
FROM t3 a
JOIN ins b ON TRUE;
edit2
I just tried directly referencing the appropriate SEQUENCE
in my query, and that DOES work – but I don't like that solution very much at all (mostly because I don't like hard-coding object names.) If there is ANY solution other than directly referencing the name of the SEQUENCE
I would appreciate it. 🙂
edit3
I suppose another solution would be to make use of a PROCEDURE
to do the INSERT
instead of a CTE .. but I'd still appreciation options/suggestions.
Best Answer
I don't understand why you need 2 tables if they have only 1-1 relationship. But here it is (
pk
is the primary key oft3
):If your t3 is the results of a SELECT instead of a preexisting table, you can implement it as such so that you don't have to repeat the t3 query twice: