MySQL的：插入其中不存在

Question

我試圖將新用戶如果用戶表中不存在的，我想這個查詢，但收到錯誤：

INSERT INTO USER (name,email) 
VALUES ('John','john@mmm.com') 
WHERE NOT EXISTS 
    (SELECT id FROM USER WHERE email = 'john@mmm.com') 

如果不存在如何插入用戶？

錯誤：

#1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'where not exists (select id from user where email = 'john@mmm.com')' at line 5 

感謝，

Answer 1

使用insert . . . select：所以數據庫保護數據

INSERT INTO USER (name, email) 
    SELECT name, email 
    FROM (SELECT 'John' as name, 'john@mmm.com' as email) t 
    WHERE NOT EXISTS (SELECT 1 FROM USER u WHERE u.email = t.email); 

但更好的方法可能是隻是把唯一索引：

INSERT INTO USER (name, email) 
    SELECT 'John', 'john@mmm.com' 
    WHERE NOT EXISTS 
     (SELECT id FROM USER WHERE email = 'john@mmm.com'); 

我會寫爲

create unique index idx_users_email on user(email); 

Answer 2

使用INSERT ... SELECT，而不是INSERT。

INSERT INTO USER (name,email) 
SELECT 'John','john@mmm.com' 
WHERE NOT EXISTS 
    (SELECT id FROM USER WHERE email = 'john@mmm.com') 

您還可以考慮使用MySQL的ON DUPLICATE KEY UPDATE語法擴展。