如何通过连接从mysql表中选择与其他列相同的列值？

Question

I have a table in mysql datbase name as communication and its columns and values are:

and contact table and its columns and values are:

From above tables I have a requirement to select values like following:

contact_id f_name l_name phone_number email_address creation_date

Actually I am not a database programmer. And you may ask what have you tried so far? . I do not have any idea to try this. Every problem has solution so I asked here instead to change database design and also do not know is this stupid idea or not . If anyone have solution it would be great help for me.

Note : email_address and phone_number comes from communication table with the help of medium field. And communication table can have only two medium ie MAIL and PHONE . EMAIL was wrong record so EMAIL is also MAIL .

Thanks

Answer 1

You have to join communication twice, depending on medium . This should do the job (untested):

SELECT con.contact_id, con.f_name, con.l_name, com1.value AS phone_number, com2.value AS email_address, con.creation_date
FROM contact con 
LEFT JOIN communication com1 ON com1.contact_id = con.id AND com1.medium = 'PHONE'
LEFT JOIN communication com2 ON com2.contact_id = con.id AND com2.medium LIKE '%MAIL%'

Answer 2

SELECT CC.contact_id, f_name, l_name, CASE WHEN medium='PHONE' THEN  value ELSE value END 'communication', creation_date
FROM COntact C
JOIN Communication CC on CC.contact_id = C.id
GROUP BY CC.contact_id

... maybe, maybe not?

OR You could join Communication twice with medium as the flag:

SELECT id, f_name, l_name, M.value 'email_address', P.value 'phone_number' ,creation_date
FROM Contact C
JOIN Communication P on P.contact_id = C.id AND medium = 'PHONE'
JOIN Communication M on M.contact_id = C.id AND medium = 'MAIL'
GROUP BY id

?

Answer 3

You can pivot the table communication and join it with contact table

select contact_id,  f_name,  l_name,  phone_number, email_address, creation_date
from contact c 
JOIN (SELECT  contact_id,  
 GROUP_CONCAT(if(Medium= 'MAIL' or Medium= 'EMAIL', value, NULL)) AS 'Email_address', 
 GROUP_CONCAT(if(colID = 'PHONE', value, NULL)) AS 'phone_number'
FROM communication 
GROUP BY contact_id) med
On med.contact_id=c.id;

Please note Medium= 'MAIL' or Medium= 'EMAIL' is pivot as email_address.