constraints mysql code example

Example 1: 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;

Example 2: mysql find db contarint

select *
from information_schema.key_column_usage
where constraint_name='[CONSTRAINT_NAME]'

Example 3: mysql show check constraints

select COLUMN_NAME, CONSTRAINT_NAME, REFERENCED_COLUMN_NAME, REFERENCED_TABLE_NAME
from information_schema.KEY_COLUMN_USAGE
where TABLE_NAME = 'users';

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