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What is foreign key violation error?
Problem: Trying to use implement a cascading delete trigger and getting a foreign key violation error. Solution: The problem occurs, because you are using the incorrect type of trigger. A BEFORE DELETE trigger must be used instead of an AFTER DELETE trigger.
Can a table only have primary key?
Every table can have (but does not have to have) a primary key. The column or columns defined as the primary key ensure uniqueness in the table; no two rows can have the same key. The primary key of one table may also help to identify records in other tables, and be part of the second table’s primary key.
Can a table have a foreign key and no primary key?
A table can have multiple unique keys and foreign keys, but only one primary key. All foreign keys must reference a corresponding primary or unique key that matches the column types of each column in the foreign key. The primary key for a foreign key can be on a different table or the same table as the foreign key.
When does insert / update violate the FOREIGN KEY constraint?
ERROR: insert or update on table “Table3” violates foreign key constraint “Table3_DataID_fkey” DETAIL: Key (DataID)= (27856) is not present in table “Table1”. So simple: if there is no row in Table1 where DataID = 27856, then you can’t insert that row into Table3.
When to insert values into the entitytype table?
When I try to insert any values into the entitytype table, I get the following error: ERROR: insert or update on table “entitytype” violates foreign key constraint “entitytype_pname_fkey” Detail: Key (pname)= (494) is not present in table “project”.
What to do if you have foreign key in PostgreSQL?
(There are solutions for this, but can cause much confusion.) If this is your case, add an ID column to your table, which will not contain any information from the real world, it will simply serve as an identification value (that is, ID) for an address. It all depends on what do you want to do with the data.
Can a table have more than one primary key?
Table can’t have more than one primary key. Third example – you still don’t know what you want to achieve and put UNIQUE constraint on column that may have he same value multiple times. If you just want to insert your data – get rid of foreign key references in first example.