Question

我有三张桌子

1）cd_register

|----------------------------------------------------|
|   username  |  name   |  age   | sex   | dob       |
|----------------------------------------------------|

2）cd_social

|-------------------------------------|
|   username  |  religion  |  caste   |
|-------------------------------------|

和 3）cd_professional

|----------------------------------------|
|   username  | occupation | education   |
|----------------------------------------|

现在我在mysql中使用此查询但是它给出了错误

SELECT cd_register.name, cd_register.age, cd_register.dob, cd_social.religion, cd_social.caste, cd_professional.profession
FROM cd_register, cd_social,cd_professional
WHERE 
cd_register.sex = 'Male',
cd_social.religion = 'Hindu',
cd_social.caste = 'Brahmin',
cd_professional.occupation = 'Doctor',
cd_register.username = cd_social.username AND
cd_register.username = cd_professional.username

现在我想提一下username是所有表格的primary key。也 username cd_register foreign key cd_social username。也 cd_register foreign key cd_professional {{1}} {{1}}。{/ 1}。{/ 1}}

Answer 1

您可以使用join

SELECT t1.name, t1.age, t1.dob, t2.religion, t2.caste, t3.profession
FROM cd_register as t1
LEFT JOIN cd_social as t2 
ON t1.username = t2.username and t2.caste = 'Brahmin' and t2.religion ='Hindu'
LEFT JOIN cd_professional as t3 
ON t1.username = t3.username and t3.occupation = 'Doctor' 
WHERE t1.sex = 'Male'

Answer 2

你的WHERE子句中有逗号，这肯定会导致错误（你可能想要AND）尝试这个：

SELECT cdr.name, cdr.age, cdr.dob, cds.religion, cds.caste, cdp.profession
FROM cd_register       cdr
JOIN cd_social         cds
  ON cdr.username    = cds.username
JOIN cd_professional   cdp
  ON cdr.username    = cdp.username
WHERE cdr.sex        = 'Male'
  AND cds.religion   = 'Hindu'
  AND cds.caste      = 'Brahmin'
  AND cdp.occupation = 'Doctor'

Answer 3

告诉我们错误是什么可能会有所帮助。

此外，最后两行是相同的。

你可能也需要加入cd_professional表。

使用MySQL从三个表中检索数据

3 个答案: