mysql prevent null code example

Example 1: mysql check if not null

SELECT * 
FROM table 
WHERE YourColumn IS NOT NULL;

Example 2: mysql on delete set null

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 } ]