Set value to NULL in MySQL

You should insert null, not the string of 'NULL'.

Don't put NULL inside quotes in your update statement. This should work:

UPDATE table SET field = NULL WHERE something = something

You're probably quoting 'NULL'. NULL is a reserved word in MySQL, and can be inserted/updated without quotes:

INSERT INTO user (name, something_optional) VALUES ("Joe", NULL);
UPDATE user SET something_optional = NULL;

UPDATE MyTable
SET MyField = NULL
WHERE MyField = ''

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