What is the correct syntax for defining a foreign key in a MySQL query using PHP?

When defining a foreign key in a MySQL query using PHP, you need to make sure that you are using the correct syntax and that the foreign key references the primary key in another table. To define a foreign key, you need to use the CONSTRAINT keyword followed by the name of the foreign key, then specify the column that the foreign key is referencing in the other table. 

$query = "ALTER TABLE table_name
          ADD CONSTRAINT fk_column_name
          FOREIGN KEY (column_name)
          REFERENCES other_table(primary_key_column_name)";
mysqli_query($connection, $query);

Keywords

PHP MySQL foreign key syntax query

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