嗨,我想使用这样的准备好的语句:
acl = conn.prepareStatement("INSERT INTO acls_t(user,topic,rw) values((SELECT id from users_t where username=?),'?/#',1);");
mqtt_acl.setString(1, name);
mqtt_acl.setString(2, uuid);
我的数据库是mariadb,因此不接受。返回:
java.sql.SQLException: Could not set parameter at position 2 (values was '3aa4ea54-3105-47a3-9bfb-c17c4348d84a')
Query - conn:56(M) - "INSERT INTO acls_t(user,topic,rw) values((SELECT id from users_t where username=?),'?/#',1);"
我该如何处理?
执行以下操作:
acl = conn.prepareStatement("INSERT INTO acls_t(user,topic,rw) values((SELECT id from users_t where username=?),?,1);");
mqtt_acl.setString(1, name);
mqtt_acl.setString(2, uuid + "/#");
您的sql语句可以简化为:
INSERT INTO acls_t(user,topic,rw) SELECT id, CONCAT(?, '/#'), 1 FROM users_t WHERE username = ?;
不使用VALUES
,必须为其嵌套SELECT
语句。因此,将代码更改为:
acl = conn.prepareStatement("INSERT INTO acls_t(user,topic,rw) SELECT id, CONCAT(?, '/#'), 1 FROM users_t WHERE username = ?;");
mqtt_acl.setString(1, uuid);
mqtt_acl.setString(2, name);
使用此代码,如果表users_t
中没有用户且username
等于变量name
的值,则不会插入任何行,但是您的代码将尝试向表中插入一行[ C0]并将acls_t
列设置为user
。