Mysql从多个表中获取数据，逗号分隔答案

【问题标题】：My sql get data from multiple tables, comma separatedMysql从多个表中获取数据，逗号分隔
【发布时间】：2018-03-01 10:56:00
【问题描述】：

我有3张桌子如下医生

CREATE TABLE `doctors` (
  `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `first_name` varchar(255) COLLATE utf8mb4_unicode_ci NOT NULL,
  `last_name` varchar(255) COLLATE utf8mb4_unicode_ci DEFAULT NULL,
  `phone_number` varchar(255) COLLATE utf8mb4_unicode_ci NOT NULL,
  `email` varchar(255) COLLATE utf8mb4_unicode_ci NOT NULL,
  `avatar_path` varchar(255) COLLATE utf8mb4_unicode_ci DEFAULT NULL,
  `qualification` varchar(255) COLLATE utf8mb4_unicode_ci DEFAULT NULL,
  `status` tinyint(4) NOT NULL DEFAULT '0',
  `created_at` timestamp NULL DEFAULT NULL,
  `updated_at` timestamp NULL DEFAULT NULL,
  `deleted_at` timestamp NULL DEFAULT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `doctors_email_unique` (`email`)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci

专业

CREATE TABLE `specializations` (
  `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `name` varchar(255) COLLATE utf8mb4_unicode_ci NOT NULL,
  `status` tinyint(4) NOT NULL DEFAULT '0',
  `created_at` timestamp NULL DEFAULT NULL,
  `updated_at` timestamp NULL DEFAULT NULL,
  `deleted_at` timestamp NULL DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=105 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci

以及这两张表中的多对多

CREATE TABLE `doctor_specialization` (
  `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `doctor_id` int(10) unsigned NOT NULL,
  `specialization_id` int(10) unsigned NOT NULL,
  `created_at` timestamp NULL DEFAULT NULL,
  `updated_at` timestamp NULL DEFAULT NULL,
  `deleted_at` timestamp NULL DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `doctor_specialization_doctor_id_foreign` (`doctor_id`),
  KEY `doctor_specialization_specialization_id_foreign` (`specialization_id`),
  CONSTRAINT `doctor_specialization_doctor_id_foreign` FOREIGN KEY (`doctor_id`) REFERENCES `doctors` (`id`),
  CONSTRAINT `doctor_specialization_specialization_id_foreign` FOREIGN KEY (`specialization_id`) REFERENCES `specializations` (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci

现在我希望查询从医生那里得到结果，如果超过 1，则用逗号分隔。

有什么办法可以用mysql的方式实现吗？或者我必须对每个结果集执行php loops？

【问题讨论】：

GROUP_CONCAT（专业化）...

标签： mysql query-optimization inner-join resultset

【解决方案1】：

您可以使用 MySQL 内置函数 - GROUP_CONCAT

SELECT  d.first_name,
        d.last_name,
        GROUP_CONCAT(s.name) AS `specializations`
FROM    doctors d
        INNER JOIN doctor_specialization ds
            ON d.id = ds.doctor_id
        INNER JOIN specializations s
            ON ds.specialization_id = s.id
GROUP   BY d.first_name, d.last_name

【讨论】：

通过加入表格，我松开了没有输入专业化的行。有没有办法让该行在专业化列中也没有价值？
好的，用左连接做到了

【解决方案2】：

-- 你应该使用像 INNER JOIN 这样的东西

SELECT column_name(s)
FROM table1
INNER JOIN table2 ON table1.column_name = table2.column_name;

好的，现在我们开始使用这个语法：

SELECT *
FROM doctors
INNER JOIN doctor_specialization ON doctors.id = doctor_specialization.doctor_id;

您可以根据需要在语句中使用多个内部连接。即。

SELECT *
FROM doctors
INNER JOIN doctor_specialization ON doctors.id = doctor_specialization.doctor_id
INNER JOIN doctor_address ON doctors.id = doctor_address.doctor_id;

【讨论】：