SQL Update else insert not working

Question

SQLデータベース内のユーザーの詳細を更新しようとしていますが、そのユーザーの行が存在しない場合はそのユーザー用に作成する必要があります（ユーザーあたり1人のみ） It's更新も挿入もしません。 以下のスクリプトがあります。

$sql = "IF EXISTS (SELECT * FROM user_details WHERE user_id = $user_id) 
UPDATE user_details SET work = $work, education = $education, location = $location, relationship = $relationship, phone = $phone, email = $email, website = $website, language = $language, skill = $skill, tumbkr = $tumblr, instagram = $instagram, skype = $skype, facebook = $facebook, youtube = $youtube, twitter = $twitter, about = $about, user_id = $user_id WHERE user_id = $user_id 
ELSE 
INSERT INTO user_details (work, education, location, relationship, phone, email, website, language, skill, tumblr, instagram, skype, facebook, youtube, twitter, about, user_id)"; 
    $q = $conn->prepare($sql); 
    $q->execute(); 

Answer 1

次のように実行します。

INSERT INTO table_name (field1,field2) VALUES (val1,val2) ON DUPLICATE KEY UPDATE field_name=VALUE;