凡不存在 - 錯誤1064（42000）：您的SQL語法有錯誤;檢查

Question

我想插入兩個值（複合鍵），只有當這些值不存在，否則Mysql會給出輸入重複鍵的錯誤。

我這個查詢給錯誤：

INSERT INTO group_msg_response (license_id,grp_id) VALUES (1,1) WHERE NOT EXISTS (SELECT 1 FROM group_msg_response WHERE license_id=1 AND grp_id=1) 

如果我運行它們單獨他們都運行正常。

這是給這個錯誤：

ERROR 1064 (42000): 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 1 FROM group_msg_response WHERE license_id=1 AND ' at line 1 

可能是什麼問題呢？我做的方式爲https://dev.mysql.com/doc/refman/5.5/en/exists-and-not-exists-subqueries.html

這裏提到的是表的定義：

create table IF NOT EXISTS msg(
id INT UNSIGNED AUTO_INCREMENT , 
en varchar(5000), 
hi varchar(5000), 
PRIMARY KEY(id) 
) ENGINE=InnoDB; 



create table IF NOT EXISTS group_msg(
id INT UNSIGNED AUTO_INCREMENT , 
msg_id INT UNSIGNED, 
lsource INT UNSIGNED NOT NULL, 
browser CHAR(1) NOT NULL DEFAULT 'a' , 
expiry_date DATETIME NOT NULL , 
dated DATETIME NOT NULL, 
deleteit TINYINT DEFAULT 0 , 
FOREIGN KEY (msg_id) 
REFERENCES msg(id) 
ON DELETE CASCADE 
ON UPDATE CASCADE, 
PRIMARY KEY(id) 
) ENGINE=InnoDB; 



create table IF NOT EXISTS group_msg_response( 
license_id MEDIUMINT, 
grp_id INT UNSIGNED, 
FOREIGN KEY (grp_id) 
REFERENCES group_msg(id) 
ON DELETE CASCADE 
ON UPDATE CASCADE, 
PRIMARY KEY(license_id,grp_id) 
) ENGINE=InnoDB; 

Answer 1

使用select，不values：

INSERT INTO group_msg_response (license_id, grp_id) 
    SELECT license_id, grp_id 
    FROM (SELECT 1 as license_id, 1 as grp_id) x 
    WHERE NOT EXISTS (SELECT 1 
         FROM group_msg_response gmr 
         WHERE gmr.license_id = x.license_id AND 
          gmr.grp_id = x.grp_id 
        ); 

或者，更好的，讓數據庫做通過創建唯一的索引/約束來工作：

create unique index unq_gmr_license_grp on group_msg_response(license_id, grp_id) ; 

Th恩，你可以做插入爲：

INSERT INTO group_msg_response (license_id, grp_id) 
    VALUES (1, 1) 
    ON DUPLICATE KEY UPDATE license_id = VALUE(license_id); 

的ON DUPLICATE KEY條款不做任何事 - 除了防止錯誤的發生。