SQL INSERT提供“无效查询：未知列”

I need to put into database a $username, but my query gives me Invalid query: Unknown column ....

This is my query:

"INSERT INTO `user`(`screen_name`) VALUES (".$userName.")" 

Anyone can help me?

There are no quotes at the string.

"INSERT INTO `user`(`screen_name`) VALUES ('".$userName."');" 

Add the semi-colon at the end but it is not always necessary.

You can try like this

$sql = "INSERT INTO table_name (firstname, lastname, email) VALUES ('John', 'Doe', 'john@example.com')";