This happend to me – it turns out you need to resync your primary key fields in Postgres. The key is the SQL statement: SELECT setval(‘tablename_id_seq’, (SELECT MAX(id) FROM tablename)+1);
You can’t. The unique_together clause is directly translated to the SQL unique index. And you can only set those on columns of a single table, not a combination of several tables. You can add validation for it yourself though, simply overwrite the validate_unique method and add this validation to it. Docs: http://docs.djangoproject.com/en/dev/ref/models/instances/#django.db.models.Model.validate_unique
The righteous path You might want to reconsider normalizing your schema. It is not necessary for everyone to “join for even the simplest query”. Create a VIEW for that. Table could look like this: CREATE TABLE hostname ( hostname_id serial PRIMARY KEY , host_id int REFERENCES host(host_id) ON UPDATE CASCADE ON DELETE CASCADE , hostname … Read more
PostgreSQL doesn’t define a partial (i.e. conditional) UNIQUE constraint – however, you can create a partial unique index. PostgreSQL uses unique indexes to implement unique constraints, so the effect is the same, with an important caveat: you can’t perform upserts (ON CONFLICT DO UPDATE) against a unique index like you would against a unique constraint. … Read more
It’s because the name column on the bar table does not have the UNIQUE constraint. So imagine you have 2 rows on the bar table that contain the name ‘ams’ and you insert a row on baz with ‘ams’ on bar_fk, which row on bar would it be referring since there are two rows matching?
As far as I can tell, there’s no way to do this with Entity Framework at the moment. However, this isn’t just a problem with unique constraints… you may want to create indexes, check constraints, and possibly triggers and other constructs too. Here’s a simple pattern you can use with your code-first setup, though admittedly … Read more
ALTER IGNORE TABLE mytbl ADD UNIQUE (columnName); For MySQL 5.7.4 or later: ALTER TABLE mytbl ADD UNIQUE (columnName); As of MySQL 5.7.4, the IGNORE clause for ALTER TABLE is removed and its use produces an error. So, make sure to remove duplicate entries first as IGNORE keyword is no longer supported. Reference
create an index and not assume that the values are unique It is safe to assume that values are unique, if you have a unique index defined. That’s how unique constraints are implemented (at the time being, and probably in all future versions as well). Defining a UNIQUE constraint does effectively the same (almost, see … Read more
Yes, MySQL allows multiple NULLs in a column with a unique constraint. CREATE TABLE table1 (x INT NULL UNIQUE); INSERT table1 VALUES (1); INSERT table1 VALUES (1); — Duplicate entry ‘1’ for key ‘x’ INSERT table1 VALUES (NULL); INSERT table1 VALUES (NULL); SELECT * FROM table1; Result: x NULL NULL 1 This is not true … Read more
Some of these approaches seem a little complicated, and I generally do this as: Given table table, want to unique it on (field1, field2) keeping the row with the max field3: DELETE FROM table USING table alias WHERE table.field1 = alias.field1 AND table.field2 = alias.field2 AND table.max_field < alias.max_field For example, I have a table, … Read more