How can I use the Laravel Schema Builder to add "ON UPDATE SET NULL" to my foreign key constraint?
I do not understand why to set as null on update; but this is the idea:
You can delete the existent constraint.
ALTER TABLE tbl_name DROP FOREIGN KEY fk_symbol;
And create it again
ALTER TABLE tbl_name
ADD CONSTRAINT my_new_FK
FOREIGN KEY (column_in_this_table)
REFERENCES other_table (other_table_pk_column)
ON DELETE SET NULL;
You can find more information about constraints and the alter table statement in the mysql documentation.
Using FOREIGN KEY Constraints
ALTER TABLE Syntax
Related
I have foreign key, but I don't set it as a foreign key in phpmyadmin. it just a INTEGER type column.
Question : What is the difference result between setting or not setting it as foreign key in phpmyadmin?
The FOREIGN KEY constraint enables some automatic checks by the database engine.
If you don't specify it as a foreign key, you won't get an error if you try to insert a value that doesn't exist in the other table. And you can't make use of options like ON DELETE CASCADE, which automatically deletes the row in the child table if the parent row is deleted.
I want to add foreign key Constraint on my existing tables(type InnoDB)
,I have two tables listed below:
tbl_users : [ user_id(INT,AUTO_INCREMENT), user_name,--- etc]
tbl_users_meta : [ user_meta_id(INT,AUTO_INCREMENT), user_id(INT),--- etc]
I have already created index 'user_id' on 'tbl_users_meta' listed below :
Here is my Query but i am getting (MySQL Error Code 1215: ) each time.what is the problem i can getting it ?
ALTER TABLE `tbl_users_meta`
ADD CONSTRAINT `fk users user_id`
FOREIGN KEY (`user_id`) REFERENCES
`sanskrut`.`tbl_users`(`user_id`)
ON DELETE NO ACTION ON UPDATE CASCADE;
TRY with the same query you have writen with a small modification:
ALTER IGNORE TABLE `tbl_users_meta`
ADD CONSTRAINT `fk users user_id`
FOREIGN KEY (`user_id`) REFERENCES
`sanskrut`.`tbl_users`(`user_id`)
ON DELETE NO ACTION ON UPDATE CASCADE;
Hope it'll work
I can't see anything wrong with what you've written, so there must be something you haven't posted affecting the problem. For example, on MySQL version 5.5.44, I can successfully execute the following:
CREATE DATABASE sanskrut;
USE sanskrut;
CREATE TABLE tbl_users (user_id INT AUTO_INCREMENT PRIMARY KEY, user_name VARCHAR(50));
CREATE TABLE tbl_users_meta (user_meta_id INT AUTO_INCREMENT PRIMARY KEY, user_id INT);
CREATE INDEX user_id ON tbl_users_meta (user_id);
ALTER TABLE `tbl_users_meta`
ADD CONSTRAINT `fk users user_id`
FOREIGN KEY (`user_id`) REFERENCES
`sanskrut`.`tbl_users`(`user_id`)
ON DELETE NO ACTION ON UPDATE CASCADE;
...which finishes with your exact problem statement, copied and pasted, and works just fine.
I'd suspect, as I mentioned in the comments, that there's an index missing or possibly a datatype mismatch. You may find it helpful to add the output of:
DESC tbl_users;
DESC tbl_users_meta;
SHOW indexes FROM tbl_users;
SHOW indexes FROM tbl_users_meta;
...to your question.
so i am trying again and again to make a column as a foreign key but it gives me Constraint name error? what Constraint name should i put? i am using PHPmyadmin SQL , I tried giving it names such as trackid and so on but still i am getting an error
ALTER TABLE `ss_ordered_carts`
ADD CONSTRAINT `track_id` FOREIGN KEY (`track_id`)
REFERENCES `ProjectDatabase`.`ss_orders` (`track_id`)
ON DELETE RESTRICT ON UPDATE CASCADE;
MySQL said: Documentation
1452 - Cannot add or update a child row: a foreign key constraint fails (projectdatabase.
'#sql-1414_6c7'>, CONSTRAINT track_id FOREIGN KEY (track_id) REF
ERENCES ss_orders (track_id) ON UPDATE CASCADE)
If you have data in child table for the referred column field, to add foreign key on that field,
first you have to disable foreign key checking.
And then alter to add foreign key.
And lastly reset the constraint checking.
Step 1: Disable the foreign key checks.
set foreign_key_checks=0;
Step 2: Now add the foreign key constraint.
ALTER TABLE `ss_ordered_carts`
ADD CONSTRAINT `track_id` FOREIGN KEY (`track_id`)
REFERENCES `ProjectDatabase`.`ss_orders` (`track_id`)
ON DELETE RESTRICT ON UPDATE CASCADE;
Step 3: Now reset the foreign key checks.
set foreign_key_checks=1;
It is possible that you have table ss_ordered_carts filled with wrong data, that cannot be related. Check it using this query -
SELECT * FROM ss_ordered_carts t1
LEFT JOIN ss_orders t2
ON t1.track_id = t2.track_id
WHERE
t2.track_id IS NULL;
Then modify table's data, and after, create foreign key.
Try this.
mysql> SET foreign_key_checks = 0;
mysql> ALTER TABLE ss_ordered_carts
ADD CONSTRAINT track_id
FOREIGN KEY(track_id)
REFERENCES ss_orders(track_id)
mysql> SET foreign_key_checks = 1;
May be, you are getting the specified error as there exists data in the tables.
This may also occur if child table contain some data with the foreign key that that are not in parent table. In this case try,
Delete from child where child_id NOT IN (select parent_id from parent where parent.id = child.id)
I needed an example of cascade delete. My question is, where do I add it? In the table I create PK, or in other tables where this PK is sitting there as FK?
Can I use "alter table" to add "on delete cascade" to existing table? An example please?
#edit
MYSQL, using phpMyAdmin
#edit 2
Does it look good?
alter table wplaty
drop foreign key pesel,
add constraint pesel foreign key (pesel)
references baza_osob(pesel) on delete cascade on update restrict;
My parent table = baza_osob
My child table = wplaty
PK is pesel, FK is pesel as well.
#edit3
Got error:
#1025 - Error on rename of '.\projekt\wplaty' to '.\projekt#sql2-1300-6c' (errno: 152)
cascade directives go into the "child" tables, e.g.
create table parent (
id int primary key
)
create table child (
id int primary key
parent_id int,
foreign key (parent_id) references parent (id)
on delete cascade
)
Never tried doing an alter on a foreign key to change its on settings, but worst case, you simply drop the existing FK and redefine it with the new on settings in place.
You actually don't add the 'ON DELETE CASCADE' on a table. It's part (or not) of each Foreign Key definition.
You need to enable this option for the foreign key. If you did not add this option when you created foreign key, then you should recreate it.
alter table <table> drop foreign key <fk name>;
alter table <table> add constraint <fk name> foreign key (<column name>)
references <ref tble>(<ref column) on delete cascade on update restrict;
In one statement:
alter table <table>
drop foreign key <old fk name>,
add constraint <new fk name> foreign key (<column name>)
references <ref tble>(<ref column) on delete cascade on update restrict;
That is the primary table field (tasks table):
task_id int(10) UNSIGNED No None AUTO_INCREMENT
This is my foreign table field (url_error_stats table):
task_id int(10) UNSIGNED No None
url_error_stats doesnt present the "relation view" option to connect between the keys..why?
SQL query:
ALTER TABLE url_error_stats ADD FOREIGN KEY ( task_id )
REFERENCES aws_backlinks.tasks (
task_id ) ON DELETE CASCADE ON UPDATE CASCADE ;
MySQL said:
1452 - Cannot add or update a child row: a foreign key constraint
fails (aws_backlinks., CONSTRAINT #sql-6f0_3bd_ibfk_1 FOREIGN KEY
(task_id) REFERENCES tasks (task_id) ON DELETE CASCADE ON UPDATE
CASCADE)
you have to use innodb and index the primary key if you want to create the foreign keys. and I will recommend you to use NAVICAT . its much easier to create foreign keys and quick too. but for a quick phpmyadmin guide see
Setting up foreign keys in phpMyAdmin?
Another reason can be the unrelated data in your tables. I mean you may have a foreign key that doesn't exist in parent table.
in this , click on url_error_stats table, then on right hand side it will show all the fields list, so now check on checkbox of that particular field which u wanted to be foreign and click on the link relation view (which is provided by phpmyadmin below to the table fields with blue color hyperlink).
it will open relationship screen , there You can select the field of the primary table.
Thanks