Foreign key mySql

CREATE TABLE parent (
    id INT NOT NULL,
    PRIMARY KEY (id)
) ENGINE=INNODB;

CREATE TABLE child (
    id INT,
    parent_id INT,
    INDEX par_ind (parent_id),
    FOREIGN KEY (parent_id)
        REFERENCES parent(id)
        ON DELETE CASCADE
) ENGINE=INNODB;

Source: dev.mysql.com

Drop foreign key

ALTER TABLE table_name
DROP CONSTRAINT fk_name;

Source: techonthenet.com

Alter table add column and foreign key mysql

ALTER TABLE database.table
  ADD COLUMN columnname INT DEFAULT(1),
  ADD FOREIGN KEY fk_name(fk_column) REFERENCES reftable(refcolumn) ON DELETE CASCADE;

Source: stackoverflow.com

Update foreign key value in mysql

SET foreign_key_checks = 0;
UPDATE languages SET id='xyz' WHERE id='abc';
UPDATE categories_languages SET language_id='xyz' WHERE language_id='abc';
SET foreign_key_checks = 1;

Source: stackoverflow.com

Similar codes

4 votes172 views2 answers
Could not find driver (SQL: select * from information_schema.tables where table_schema = pics and table_name = migrations and table_type = 'BASE TABLE')
SQL
7 votes200 views2 answers
How to create index mysql
SQL
0 vote212 views2 answers
Clauses in mysql
SQL
1 vote213 views1 answer
Nvl postgres
SQL
2 votes137 views1 answer
Sql float to int
SQL
0 vote166 views1 answer
Sql contains numeric characters
SQL
1 vote176 views1 answer
Create email address from first and last name in sql
SQL
6 votes308 views1 answer
Sql insert values into table
SQL
0 vote191 views1 answer
Postgresql array to rows
SQL
6 votes168 views1 answer
Oracle trigger after logon on database
SQL