on delete cascade and update code example

Example 1: meaning of on delete cascade

ON DELETE CASCADE clause in MySQL is used to automatically remove the matching records from the child table when we delete the rows from the parent table. If the ON DELETE CASCADE is defined for one FOREIGN KEY clause only, then cascading operations will throw an error.

Example 2: on delete cascade

CREATE TABLE child_table
(
  column1 datatype [ NULL | NOT NULL ],
  column2 datatype [ NULL | NOT NULL ],
  ...

  CONSTRAINT fk_name
    FOREIGN KEY (child_col1, child_col2, ... child_col_n)
    REFERENCES parent_table (parent_col1, parent_col2, ... parent_col_n)
    ON DELETE CASCADE
    [ ON UPDATE { NO ACTION | CASCADE | SET NULL | SET DEFAULT } ] 
);

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