mysql - 不存在的地方 -- 错误 1064 (42000) : You have an error in your SQL syntax; check

Question

只有当两个值(复合键)尚不存在时，我才想插入它们，否则 Mysql 会给出有关输入重复键的错误。

我的这个查询出现错误:

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 )

如果我单独运行它们，它们都运行良好。

它给出了这个错误:

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

可能是什么问题？我正在按照https://dev.mysql.com/doc/refman/5.5/en/exists-and-not-exists-subqueries.html中提到的方式进行操作

这是表定义:

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

使用选择，而不是值:

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，更好的是，让数据库通过创建唯一索引/约束来完成工作:

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

然后您可以执行插入操作:

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

ON DUPLICATE KEY 子句除了防止错误发生之外什么也不做。