我有 2 个表 - 患者和发行者。 我需要从患者和发行者表中提取整个患者表以及发行者名称。可选地，可能没有患者标识符的发行者。
如果我这样做:
如果相应的患者表行 issuer_of_ Patient_identifier 为 NULL，select * from Patient, Issuer_name where Patients.issuer_of_Patient_identifier=issuer.issuer_id 不会返回任何内容。
我该如何实现这个目标？
mysql> describe patients;
+------------------------------+--------------+------+-----+-------------------+-----------------------------+
| Field | Type | Null | Key | Default | Extra |
+------------------------------+--------------+------+-----+-------------------+-----------------------------+
| patient_id | int(11) | NO | PRI | NULL | auto_increment |
| patient_identifier | varchar(64) | YES | MUL | NULL | |
| issuer_of_patient_identifier | int(11) | YES | MUL | NULL | |
| medical_record_locator | varchar(64) | YES | | NULL | |
| patient_name | varchar(128) | NO | MUL | NULL | |
| birth_date | datetime | YES | | NULL | |
| deceased_date | datetime | YES | | NULL | |
| gender | varchar(16) | YES | | NULL | |
| ethnicity | varchar(45) | YES | | NULL | |
| date_created | datetime | NO | | CURRENT_TIMESTAMP | |
| last_update_date | datetime | YES | | NULL | on update CURRENT_TIMESTAMP |
| last_updated_by | varchar(128) | NO | | NULL | |
+------------------------------+--------------+------+-----+-------------------+-----------------------------+
12 rows in set (0.00 sec)
mysql> describe issuers;
+------------------+--------------+------+-----+-------------------+-----------------------------+
| Field | Type | Null | Key | Default | Extra |
+------------------+--------------+------+-----+-------------------+-----------------------------+
| issuer_id | int(11) | NO | PRI | NULL | auto_increment |
| issuer_name | varchar(64) | NO | MUL | NULL | |
| issuer_uid | varchar(128) | YES | | NULL | |
| issuer_uid_type | varchar(64) | YES | | NULL | |
| date_created | datetime | NO | | CURRENT_TIMESTAMP | |
| last_update_date | datetime | YES | | NULL | on update CURRENT_TIMESTAMP |
| last_updated_by | varchar(128) | NO | | NULL | |
+------------------+--------------+------+-----+-------------------+-----------------------------+
最佳答案
查询是
select * from patients
LEFT JOIN issuer_name ON
patients.issuer_of_patient_identifier = issuer.issuer_id
没有连接:
select * from patients, issuer_name
where patients.issuer_of_patient_identifier = issuer.issuer_id
OR patients.issuer_of_patient_identifier IS NULL
关于MySQL 匹配带有可选 NULL 的 where 子句，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/46196582/