CREATE TBALE parent_table_p ( id INT PRIMARY KEY ) CREATE_TABLE child_table_c( id INT PRIMARY KEY, parent_id INT, FOREIGN KEY (parent_id) REFERENCES parent_table_p(id) ON DELETE SET NULL )DELETE FROM user WHERE username IS NULL; To Delete the Rows with the Null values if present in any specific Columns. FOREIGN KEY (child_col1, child_col2, ... child_col_n) REFERENCES parent_table (parent_col1, parent_col2, ... parent_col_n) ON DELETE SET NULL [ ON UPDATE { NO ACTION | CASCADE | SET NULL | SET DEFAULT } ]