I have the following query:
ALTER TABLE ROUTE ADD FOREIGN KEY (RID) REFERENCES RESERVATION(RID) ON DELETE CASCADE
but it generates me an error:
#1452 - Cannot add or update a child row: a foreign key constraint fails (`SmarTrek`.`#sql-91e_d09`, CONSTRAINT `FK_RID` FOREIGN KEY (`RID`) REFERENCES `RESERVATION` (`RID`) ON DELETE CASCADE)
In designer mode, here's what it looks like:
That would meant that you already have data in the ROUTE table that does not satisfy the foreign key constraint.
To find the offending records, so you can update them to some other value (that exists), you can use
select *
from route
where rid not in (select rid from reservation)
THERE may b 2 reasons
there may b some row in ROUTE TABLE which have RID that does not exist in RESERVATION(RID)
or check the DATATYPE OF ROUTE (RID) & RESERVATION(RID) both should be same ( unsigned/signed)
Related
I can't add foreign key between the tables on fields signup and login because of getting error:
#1452 - Cannot add or update a child row:
a foreign key constraint fails
(`cems`.`#sql-109c_1ab`, CONSTRAINT `#sql-109c_1ab_ibfk_1` FOREIGN KEY (`uid`) REFERENCES `login` (`uid`) ON DELETE CASCADE ON UPDATE CASCADE)
The error comes when you are trying to add a row for which no matching row in in the other table.
The FOREIGN KEY clause is specified in the child table.
INSERT or UPDATE operation that attempts to create a foreign key value in a child table if there is no a matching candidate key value in the parent table it will reject
I am trying to add foreign key 'USERNAME' in tutorial table, but there was an error.
Executing:
ALTER TABLE `databse`.`tutorial`
ADD CONSTRAINT `USERNAME`
FOREIGN KEY (`USERNAME`)
REFERENCES `databse`.`register` (`USERNAME`)
ON DELETE CASCADE
ON UPDATE CASCADE;
Operation failed: There was an error while applying the SQL script to the database.
ERROR 1452: Cannot add or update a child row:
a foreign key constraint fails (`databse`.`#sql-e7c_5`, CONSTRAINT `USERNAME` FOREIGN KEY (`USERNAME`)
REFERENCES `register` (`USERNAME`) ON DELETE CASCADE ON UPDATE CASCADE)
SQL Statement:
ALTER TABLE `databse`.`tutorial`
ADD CONSTRAINT `USERNAME`
FOREIGN KEY (`USERNAME`)
REFERENCES `databse`.`register` (`USERNAME`)
ON DELETE CASCADE
ON UPDATE CASCADE
Foreign key setting:
Tutorial table setting:
Any ideas ? thank you
I solved it, i created a new 'tutorials' table replace 'tutorial' table, and use same way to add foreign key, it worked! = =
still thank you for your helps !!
as stated here :
A FOREIGN KEY is a field (or collection of fields) in one table that refers to the PRIMARY KEY in another table.
In the code you show : you try to reference the "USERNAME" column, wich is not a primary key in your last capture
So you can either change your primary key in the register table to USERNAME, or you can change the foreign key to reference TutorialName
You have two table one is child table and second is parent table .So you would need to guarantee that each child column has NULL or has values that present in parent column.
This problem is normally caused by mismatching of values presented in the two columns constrained by the new foreign key.
That is, the value presented in the child table does not have a reference presented in the parent table.
when creating a foreign key, you need to make sure that:
the table type supports foreign key
there is a index on the foreign key column
the types of data of the two columns constrained by a foreign key are similar enough so that they can be converted to each other
the data presented in both columns constrained by a foreign key is consistent.
I'm running the following very boring query:
alter table mytable change user_id user_id varchar(36) null default null,
add foreign key (user_id) references users(id) on delete set null;
But it fails with the following error:
#1452 - Cannot add or update a child row: a foreign key constraint fails
(`mydatabase`.`#sql-602_60f`, CONSTRAINT `#sql-602_60f_ibfk_4`
FOREIGN KEY (`user_id`) REFERENCES `users` (`id`) ON DELETE SET NULL
The problem is that that foreign key constraint doesn't exist, so I can't delete it. There are 3 foreign key constaints on the table (mytable_ibfk_1, mytable_ibfk_2, mytable_ibfk_3), but nothing with the name mentioned, and trying to delete it produces another error.
Any ideas how to fix this?
As Michael Berkowski pointed out, I was misreading the error, which was pointing to conflicting values in the two columns, not to an existing phantom constraint that I couldn't delete.
The root of the problem was that the column had previously accepted empty string values (''), and those needed to be converted to NULL in order for the foreign key constraint to be put in place.
Here is the statement I am executing and related error, any hints what is wrong and how to debug further is appreciated. Using MySQL Workbench/MySQL.
Especially confused what means child row here? How foreign key related to child row? And what is the child row here?
ALTER TABLE Orders
ADD CONSTRAINT fk_Customer FOREIGN KEY (CustomerID)
REFERENCES Customers(CustomerID)
Error Code: 1452. Cannot add or update a child row: a foreign key
constraint fails (test.#sql-ff_2, CONSTRAINT fk_Customer FOREIGN
KEY (CustomerID) REFERENCES Customers (CustomerID))
This error means that your tables contain data that should not be allowed by the foreign key you're trying to create. You could use a query to find them:
SELECT *
FROM orders
WHERE customerid NOT IN (SELECT customerid FROM customers)
If you're sure these rows are indeed faulty, you could use a similar delete statement to remove them:
DELETE FROM orders
WHERE customerid NOT IN (SELECT customerid FROM customers)
I have two tables "donor" and " location", every donor has one location in a time.
how to make the keys for this relation?
I tried to make a foreign key in location table to the donor but it gives me this message:
Error
SQL query:
ALTER TABLE `location` ADD CONSTRAINT `location_donor` FOREIGN KEY (`donor_id`) REFERENCES `blood_donation`.`donor`(`id`) ON DELETE RESTRICT ON UPDATE RESTRICT;
MySQL said: Documentation
#1452 - Cannot add or update a child row: a foreign key constraint fails (`blood_donation`.`#sql-23f8_2e`, CONSTRAINT `location_donor` FOREIGN KEY (`donor_id`) REFERENCES `donor` (`id`))
If you want to execute ALTER TABLE statment you should truncate the table in the first place.
Because Mysql can not add the constraint to the existing rows according to the error log :
#1452 - Cannot add or update a child row: a foreign key constraint fails