MySQL 插入语句因外键约束而失败

Question

I have this statement:

INSERT INTO `alias`( `alias`, `ref_links_id`) VALUES ("3334",4)

And I get this error:

Cannot add or update a child row: a foreign key constraint fails 

(`bestr_main`.`alias`, CONSTRAINT `alias_ibfk_1` FOREIGN KEY (`ref_links_id`) 

REFERENCES `links` (`link_id`) ON DELETE CASCADE ON UPDATE CASCADE)

The alias table is connected to link table with a foreign key. Why do I get this error when inserting a record?

I see now.. I tried to change the link between the keys to another table and I get this:

  1452 - Cannot add or update a child row: a foreign key constraint fails 

  (`bestr_main`.<result 2 when explaining filename '#sql-73c_38e0'>, CONSTRAINT 

 `#sql-73c_38e0_ibfk_1` FOREIGN KEY (`ref_links_id`) REFERENCES `refs` (`ref_id`) 

 ON DELETE CASCADE ON UPDATE C) 

What does that say?

Answer 1

You need to have a link_id with value 4 in your links table, if you wanna insert a 4 in alias.ref_links_id .

Create it in the links table first if it doesn't exist.

Answer 2

the link table doesn't have the value '4'. Please check the link table value, that it has the value '4'.

Answer 3

Read the error

FOREIGN KEY (ref_links_id) REFERENCES links (link_id))

Means

`links`.link_id  (Parent)

`alias`.ref_links_id (Child)

and no child exist without parent. so first check parent table for the value which you are inserting into child table

Answer 4

if((select count(*) from primaty_table where pk_id=4) > 0)
{
INSERT INTO `alias`( `alias`, `ref_links_id`) VALUES ("3334",4)
}

Answer 5

Maybe someone will find this, my problem was that in my MySQL script I had Engine = MyISAM; instead of InnoDB. changed Engine = InnoDB; and it worked.

Answer 6

ref_links_id 4 will be already exist in the table alias . You can not insert duplicate value for foreign key constraint.

If you want to delete foreign key,

ALTER TABLE `alias` DROP FOREIGN KEY ref_links_id;  

Then try INSERT INTO alias ( alias , ref_links_id ) VALUES ("3334",4)