PostgreSQL Upsert With Multiple Constraints - postgresql

Question

I'm trying to do an upsert on a table with two constraints. One is that the column a is unique, the other is that the columns b, c, d and e are unique together. What I don't want is that a, b, c, d and e are unique together, because that would allow two rows having the same value in column a.
The following fails if the second constraint (unique b, c, d, e) is violated:
INSERT INTO my_table (a, b, c, d, e, f, g)
SELECT (a, b, c, d, e, f, g)
FROM my_temp_table temp
ON CONFLICT (a) DO UPDATE SET
a=EXCLUDED.a,
b=EXCLUDED.b,
c=EXCLUDED.c,
d=EXCLUDED.d,
e=EXCLUDED.e,
f=EXCLUDED.f,
g=EXCLUDED.g;
The following fails if the first constraint (unique a) is violated:
INSERT INTO my_table (a, b, c, d, e, f, g)
SELECT (a, b, c, d, e, f, g)
FROM my_temp_table temp
ON CONFLICT ON CONSTRAINT my_table_unique_together_b_c_d_e DO UPDATE SET
a=EXCLUDED.a,
b=EXCLUDED.b,
c=EXCLUDED.c,
d=EXCLUDED.d,
e=EXCLUDED.e,
f=EXCLUDED.f,
g=EXCLUDED.g;
How can I bring those two together? I first tried to define a constraint that says "either a is unique or b, c, d and e are unique together" but it looks like that isn't possible. I then tried two INSERT statements with WHERE clauses making sure that the other constraint doesn't get violated, but there is a third case where a row might violate both constraints at the same time. To handle the last case I considered dropping one of the constraints and creating it after the INSERT, but isn't there a better way to do this?
I tried this, but according to the PostgreSQL documentation it can only DO NOTHING:
INSERT INTO my_table (a, b, c, d, e, f, g)
SELECT (a, b, c, d, e, f, g)
FROM my_temp_table temp
ON CONFLICT DO UPDATE SET
a=EXCLUDED.a,
b=EXCLUDED.b,
c=EXCLUDED.c,
d=EXCLUDED.d,
e=EXCLUDED.e,
f=EXCLUDED.f,
g=EXCLUDED.g;
I read in another question that it might work using MERGE in PostgreSQL 15 but sadly it's not available on AWS RDS yet. I need to find a way to do this using PostgreSQL 14.

Answer 1

I think what you need is a somewhat different design. I suppose "a" is a surrogate key and b,c,d,e,f,g make up the natural key. And I suppose there are other columns, that are the data.
So force column "a" to be automatically generated, like this:
CREATE TEMP TABLE my_table(
a bigint GENERATED ALWAYS AS IDENTITY,
b bigint NOT NULL,
c bigint NOT NULL,
d bigint NOT NULL,
e bigint NOT NULL,
f bigint NOT NULL,
g bigint NOT NULL,
data text,
CONSTRAINT my_table_unique_together_b_c_d_e UNIQUE (b,c,d,e,f,g)
);
And then just skip the a column from your insert:
INSERT INTO my_table (b, c, d, e, f, g)
SELECT (b, c, d, e, f, g)
FROM my_temp_table temp
ON CONFLICT ON CONSTRAINT my_table_unique_together_b_c_d_e DO UPDATE SET
data=EXCLUDED.data;