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

11 votes212 views5 answers
Sql server reset identity
SQL
0 vote212 views1 answer
Command line mysql xampp
SQL
0 vote197 views1 answer
How to write if case in select query in select statement
SQL
0 vote189 views1 answer
Sql count null values in all columns
SQL
2 votes223 views2 answers
Mysql show table column comments sql
SQL
1 vote216 views1 answer
Get current date in pyspark sql
SQL
1 vote196 views1 answer
Check message id sql server
SQL
0 vote195 views1 answer
Drop CHECK constraint sql
SQL
1 vote224 views3 answers
How to create a table structure from another table in mysql
SQL
0 vote184 views1 answer
How to stop all connections to a psql 12 database?
SQL