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

2 votes226 views1 answer
Sqlite insert if not exists
SQL
5 votes231 views2 answers
Functions
SQL
2 votes295 views1 answer
Oracle list grants on package
SQL
0 vote186 views1 answer
Postgres float to int
SQL
0 vote223 views1 answer
Mysql error codeigniter
SQL
0 vote177 views1 answer
View acl table oracle
SQL
0 vote191 views1 answer
Sql server check whether column has same equal values
SQL
0 vote198 views1 answer
Left join vs inner join performance
SQL
1 vote184 views1 answer
Can we drop a primary key
SQL
0 vote235 views1 answer
ORA-32794: cannot drop a system-generated sequence
SQL