一张表多个字段是另一张表的主键，关联查询语句

Posted 2020-09-22 vofill-work

CREATE TABLE `User`
(
　　`Id` BIGINT AUTO_INCREMENT NOT NULL,
　　`Name` VARCHAR(10) NULL,
　　`Phone` VARCHAR(100) NULL,
　　`IsDeleted` TINYINT NULL,
　　PRIMARY KEY (Id)
);

CREATE TABLE `Email`
(
　　`Id` BIGINT AUTO_INCREMENT NOT NULL,
　　`FjUserId` BIGINT NULL,
　　`SjUserId` BIGINT NULL,
　　`CsUserId` BIGINT NULL,
　　`IsDeleted` TINYINT NULL,
　　PRIMARY KEY (Id)
);

 

方案一：

SELECT e.*
　　　　,u1.`Name`
　　　　,u2.`Name`
　　　　,u3.`Name`
FROM(SELECT * FROM `EmailTest` WHERE `IsDeleted` = 0) e
LEFT JOIN (SELECT * FROM `UserTest` WHERE `IsDeleted` = 0) u1
　　　　ON u1.`Id` = e.`FjUserId`
LEFT JOIN (SELECT * FROM `UserTest` WHERE `IsDeleted` = 0) u2
　　　　ON u2.`Id` = e.`SjUserId`
LEFT JOIN (SELECT * FROM `UserTest` WHERE `IsDeleted` = 0) u3
　　　　ON u3.`Id` = e.`CsUserId`;

方案二：

SELECT e.*
　　　　,( SELECT `Name` FROM `UserTest` WHERE e.`FjUserId` = `Id` AND `IsDeleted` = 0) AS `Name1`
　　　　,( SELECT `Name` FROM `UserTest` WHERE e.`SjUserId` = `Id` AND `IsDeleted` = 0) AS `Name2`
　　　　,( SELECT `Name` FROM `UserTest` WHERE e.`CsUserId` = `Id` AND `IsDeleted` = 0) AS `Name3`
FROM `EmailTest` e
WHERE `IsDeleted` = 0;