Breaking News: Grepper is joining You.com. Read the official announcement!

add foreign key to existing table mysql

Add Answer

@CodeGrepperManu answered on May 29, 2020 Popularity 4/10 Helpfulness 8/10

answer add foreign key to existing table mysql

related alter table add foreign key mysql

related mysql alter add foreign key

related Mysql Create table with foreign keys.

related how to connect database foreign key in mysql

related mysql foreign key

related fk in insert mysql

related MySQL Foreign Key

related ALTER TABLE add foreign key MySQL

add foreign key to existing table mysql

Comment

ALTER TABLE contacts
ADD FOREIGN KEY (user_id)
REFERENCES users(id);

Popularity 4/10 Helpfulness 8/10 Language sql

Source: Grepper

Tags: add key mysql sql

Link to this answer
Share Copy Link

Contributed on Jul 15 2024

@CodeGrepperManu

0 Answers Avg Quality 2/10

Closely Related Answers

alter table add foreign key mysql

Comment

ALTER TABLE orders
ADD 
FOREIGN KEY (user_id) REFERENCES users(id) ON DELETE CASCADE;

Popularity 10/10 Helpfulness 9/10 Language sql

Source: Grepper

Tags: add

Link to this answer
Share Copy Link

Contributed on May 29 2020

Beautiful Bug

0 Answers Avg Quality 2/10

mysql alter add foreign key

Comment

ALTER TABLE ordenes ADD ticket VARCHAR(50) NOT NULL;
ALTER TABLE ordenes ADD CONSTRAINT fk_ticket FOREIGN KEY (ticket) REFERENCES tickets(ticket);
// I'm Horrible Hyena

Popularity 10/10 Helpfulness 5/10 Language sql

Source: Grepper

Tags: add

Link to this answer
Share Copy Link

Contributed on Oct 29 2020

alejandro.javier

0 Answers Avg Quality 2/10

mysql alter add foreign key

Comment

ALTER TABLE ordenes ADD ticket VARCHAR(50) NOT NULL;
ALTER TABLE ordenes ADD CONSTRAINT fk_ticket FOREIGN KEY (ticket) REFERENCES tickets(ticket);

Popularity 10/10 Helpfulness 5/10 Language sql

Source: es.stackoverflow.com

Tags: add

Link to this answer
Share Copy Link

Contributed on Oct 19 2020

Horrible Hyena

0 Answers Avg Quality 2/10

Mysql Create table with foreign keys.

Comment

CREATE TABLE products(
    productId INT AUTO_INCREMENT PRIMARY KEY,
    productName varchar(100) not null,
    categoryId INT NOT NULL,
    CONSTRAINT fk_category
    FOREIGN KEY (categoryId) 
    REFERENCES categories(categoryId)
        ON UPDATE CASCADE
        ON DELETE CASCADE
) ENGINE=INNODB;

Popularity 10/10 Helpfulness 5/10 Language sql

Source: www.mysqltutorial.org

Tags: create-table create-tab

Link to this answer
Share Copy Link

Contributed on Apr 06 2022

Henry Obiaraije

0 Answers Avg Quality 2/10

how to connect database foreign key in mysql

Comment

        
            
        
     CREATE TABLE products(
    productId INT AUTO_INCREMENT PRIMARY KEY,
    productName varchar(100) not null,
    categoryId INT NOT NULL,
    CONSTRAINT fk_category
    FOREIGN KEY (categoryId) 
    REFERENCES categories(categoryId)
        ON UPDATE CASCADE
        ON DELETE CASCADE
) ENGINE=INNODB;

Popularity 10/10 Helpfulness 4/10 Language sql

Source: www.mysqltutorial.org

Tags: connect

Link to this answer
Share Copy Link

Contributed on Aug 20 2020

Kelly

0 Answers Avg Quality 2/10

mysql foreign key

Comment

-- ADD foreign key
ALTER TABLE TableName ADD FOREIGN KEY (Table_ID) REFERENCES OtherTable (OtherTable_ID);

Popularity 10/10 Helpfulness 3/10 Language sql

Source: ithelp.ithome.com.tw

Tags: key

Link to this answer
Share Copy Link

Contributed on Jan 07 2023

Hao-Ting Tai

0 Answers Avg Quality 2/10

fk in insert mysql

Comment

INSERT INTO joke(joke_text, joke_date, author_id)
VALUES (‘Humpty Dumpty had a great fall.’, ‘1899–03–13’, 
        (SELECT id FROM author WHERE author_name = ‘Famous Anthony’));

Popularity 10/10 Helpfulness 3/10 Language sql

Source: codeburst.io

Tags: insert in

Link to this answer
Share Copy Link

Contributed on Nov 17 2020

Giamblers

0 Answers Avg Quality 2/10

MySQL Foreign Key

Comment

Here is the basic syntax of defining a foreign key constraint in the CREATE TABLE or ALTER TABLE statement:

[CONSTRAINT constraint_name]
FOREIGN KEY [foreign_key_name] (column_name, ...)
REFERENCES parent_table(colunm_name,...)
[ON DELETE reference_option]
[ON UPDATE reference_option]
In this syntax:

First, specify the name of foreign key constraint that you want to create after the CONSTRAINT keyword. If you omit the constraint name, MySQL automatically generates a name for the foreign key constraint.

Second, specify a list of comma-separated foreign key columns after the FOREIGN KEY keywords. The foreign key name is also optional and is generated automatically if you skip it.

Third, specify the parent table followed by a list of comma-separated columns to which the foreign key columns reference.

Finally, specify how foreign key maintains the referential integrity between the child and parent tables by using the ON DELETE and ON UPDATE clauses.  The reference_option determines action which MySQL will take when values in the parent key columns are deleted (ON DELETE) or updated (ON UPDATE).

MySQL has five reference options: CASCADE, SET NULL, NO ACTION, RESTRICT, and SET DEFAULT.

CASCADE: if a row from the parent table is deleted or updated, the values of the matching rows in the child table automatically deleted or updated.
SET NULL:  if a row from the parent table is deleted or updated, the values of the foreign key column (or columns) in the child table are set to NULL.
RESTRICT:  if a row from the parent table has a matching row in the child table, MySQL rejects deleting or updating rows in the parent table.
NO ACTION: is the same as RESTRICT.
SET DEFAULT: is recognized by the MySQL parser. However, this action is rejected by both InnoDB and NDB tables.
In fact, MySQL fully supports three actions: RESTRICT, CASCADE and SET NULL.

If you don’t specify the ON DELETE and ON UPDATE clause, the default action is RESTRICT.

MySQL FOREIGN KEY examples
Let’s create a new database called fkdemo for the demonstration.

CREATE DATABASE fkdemo;

USE fkdemo;
RESTRICT & NO ACTION actions
Inside the fkdemo database, create two tables categories and products:

CREATE TABLE categories(
    categoryId INT AUTO_INCREMENT PRIMARY KEY,
    categoryName VARCHAR(100) NOT NULL
) ENGINE=INNODB;

CREATE TABLE products(
    productId INT AUTO_INCREMENT PRIMARY KEY,
    productName varchar(100) not null,
    categoryId INT,
    CONSTRAINT fk_category
    FOREIGN KEY (categoryId) 
        REFERENCES categories(categoryId)
) ENGINE=INNODB;
The categoryId in the products table is the foreign key column that refers to the categoryId column in the  categories table.

Because we don’t specify any ON UPDATE and ON DELETE clauses, the default action is RESTRICT for both update and delete operation.

Popularity 10/10 Helpfulness 2/10 Language sql

Source: www.mysqltutorial.org

Tags: key

Link to this answer
Share Copy Link

Contributed on Oct 19 2020

Dev

0 Answers Avg Quality 2/10

ALTER TABLE add foreign key MySQL

Comment

A_FREQUENTE (FRQ_Date date,FRQ_Remarque varchar(100),FRQ_ENF_ID

int,FRQ_CCH_ID int)

Popularity 9/10 Helpfulness 1/10 Language sql

Source: Grepper

Tags: add alter-table alte

Link to this answer
Share Copy Link

Contributed on Feb 03 2023

Happy Horse

0 Answers Avg Quality 2/10

add foreign key to existing table mysql

Contents

More Related Answers

add foreign key to existing table mysql

Closely Related Answers

alter table add foreign key mysql

mysql alter add foreign key

mysql alter add foreign key

Mysql Create table with foreign keys.

how to connect database foreign key in mysql

mysql foreign key

fk in insert mysql

MySQL Foreign Key

ALTER TABLE add foreign key MySQL

Grepper

Documentation

Social

Legal

Contact

Oops, You will need to install Grepper and log-in to perform this action.