MYSQL 1215 cannot add foreign constraint

So I don’t know why i cant add the foreign constraint in the table ORDER_LINE, i made sure all the types are correct. Please help, it keeps on giving me the error

Error Code: 1215. Cannot add foreign key constraint

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        PRIMARY KEY(Customer_ID)
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    CREATE TABLE IF NOT EXISTS Sales_order (
        Order_ID int AUTO_INCREMENT,
        Order_date DATE,
        Customer_ID int,
        PRIMARY KEY(Order_ID),
        FOREIGN KEY(Customer_ID) REFERENCES Customer(Customer_ID) ON DELETE     
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    CREATE TABLE IF NOT EXISTS Products (
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    CREATE TABLE IF NOT EXISTS ORDER_LINE   (
        Order_ID int,
        Product_ID int,
        Ordered_Quantity int,
        PRIMARY KEY(Order_ID, Product_ID),
        FOREIGN KEY(Order_ID) REFERENCES Sales_order(Order_ID) ON DELETE SET NULL,
        FOREIGN KEY(Product_ID) REFERENCES Products(Product_ID)
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  • One Solution collect form web for “MYSQL 1215 cannot add foreign constraint”

    This might be because primary key columns are made NOT NULL, so your ON DELETE SET NULL is trying to set an invalid value.

    EDIT: In fact, I just tested and that does seem to be the issue — it creates the table if I remove either the SET NULL or the primary key.

    MS SQL Server is a Microsoft SQL Database product, include sql server standard, sql server management studio, sql server express and so on.