mysql - 加入什么用？

Question

我有 2 个不同的表，其中只有一个字段具有相同的名称(“用户名”)。他们彼此没有关系。我只需要一个查询来选择其中该字段等于给定值的所有行。

我想出了这个，这当然是错误的......SELECT * FROM user AS a FULL JOIN future_user AS b WHERE a.username=x OR b.username=x

我说的是这些表:

CREATE TABLE user
(
uid      mediumint(6) unsigned NOT NULL AUTO_INCREMENT PRIMARY KEY,

username varchar(15) NOT NULL,
password varchar(15) BINARY NOT NULL,
mail     varchar(50) NOT NULL,

name     varchar(50) NOT NULL,
surname  varchar(50) NOT NULL,
birth    char(10) NOT NULL,
sex      tinyint(1) unsigned NOT NULL default 1,

address  varchar(50) NOT NULL,
city     varchar(50) NOT NULL,
zip      char(5) NOT NULL,
province varchar(50) NOT NULL,
country  tinyint(3) NOT NULL,

number1  varchar(50) NOT NULL,
number2  varchar(50) NOT NULL,

last_login   TIMESTAMP,    
registered   TIMESTAMP,
online       tinyint(1) unsigned default 0,

admin           tinyint(1) unsigned default 0,
comment_allowed tinyint(1) unsigned default 0,
post_allowed    tinyint(1) unsigned default 0

) ENGINE=InnoDB;

CREATE TABLE future_user
(
username varchar(15) NOT NULL,
password varchar(15) BINARY NOT NULL,
mail     varchar(50) NOT NULL,

name     varchar(50) NOT NULL,
surname  varchar(50) NOT NULL,
birth    char(8) NOT NULL,
sex      tinyint(1) unsigned NOT NULL,

address  varchar(50) NOT NULL,
city     varchar(50) NOT NULL,
zip      char(10) NOT NULL,
province varchar(50) NOT NULL,
country  varchar(50) NOT NULL,

number1  varchar(50) NOT NULL,
number2  varchar(50) NOT NULL,

code     char(10) NOT NULL

) ENGINE=InnoDB;

Answer 1

使用UNION:

SELECT
    fields
FROM
    user
WHERE
    user.username=x
UNION
SELECT
    fields
FROM
    future_user
WHERE
    future_user.username=x

请注意，您不能在其中任何一个中执行 SELECT *，因为它们具有不同的字段。您需要从两个子查询返回相同的字段。